# 6L6 for 6V6 power tubes



## GTmaker (Apr 24, 2006)

Hi Folks...
In case you didnt know I live in Guelph Ontario...I just tested all the tubes in my "used" Fender Deluxe Reverb with my Jackson 648 tube tester. 

Basicaly, the 6V6 power tubes are weak ( or not as strong as they should be.)
In my pased life I owned a Fender 59' Bassman and a wonderfull Super Reverb ri.
This has left me with 3 sets of 95-100 percent 6L6 power tubes that are quietly sitting in a box.

Bottom line....hopefully someone local has a decent set of 6V6 power tubes that they can trade me for a set of 6L6 power tubes.

I will be willing to make a small trip to make this happen...

let me know what you got.
G.


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## greco (Jul 15, 2007)

You might get a better response/exposure in the 
"For Sale, Trade or Wanted Section...Amps, Cabs and Speakers using the FT prefix









Just a thought . GLW TRADE


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## KapnKrunch (Jul 13, 2016)

Need "Gold" to trade @greco?


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## greco (Jul 15, 2007)

KapnKrunch said:


> Need "Gold" to trade @greco?


OOOOPS...good catch!
@GTmaker Cough up the twenty bucks you cheap old bugger.
We are ...or were...friends...LOL


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## GTmaker (Apr 24, 2006)

KapnKrunch said:


> Need "Gold" to trade @greco?


so I just found out my membership expired...I use paypal for the annual fee and its in the process of transferring money from my bank account to paypal.
This post was option # 2....
G.


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## _Knighthawk_ (Mar 2, 2014)

Mine expired recently. The only reason I noticed was because I started seeing ads...which I thought weird. Then I tried to post something for sale...which is when it hit me: I am seeing ads cuz my membership expired. DOH!


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## StevieMac (Mar 4, 2006)

What if you tried a set of 6L6's in you DR instead? I know it can be done with a rebias, although my understanding is that the "safest" approach is to use a plug-in SS rectifier at the same time. Best to check _first_ with others more experienced than I however.


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## GTmaker (Apr 24, 2006)

StevieMac said:


> What if you tried a set of 6L6's in you DR instead? I know it can be done with a rebias, although my understanding is that the "safest" approach is to use a plug-in SS rectifier at the same time. Best to check _first_ with others more experienced than I however.


interesting option....if I do try it, would you know what bias settings the 6L6 would be safest at?
I do have a bias tester but not a SS rectifier.
G.


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## StevieMac (Mar 4, 2006)

GTmaker said:


> interesting option....if I do try it, would you know what bias settings the 6L6 would be safest at?
> I do have a bias tester but not a SS rectifier.
> G.



This may be helpful: Tube Bias Calc 
Depending on the sweep of your bias pot, you'll likely be somewhere at the low end of recommended bias. In my experience, simply popping a set of 6L6's into an amp that's been set up for 6V6s usually leaves bias sitting on the cool end of the spectrum...


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## GTmaker (Apr 24, 2006)

GTmaker said:


> interesting option....if I do try it, would you know what bias settings the 6L6 would be safest at?
> I do have a bias tester but not a SS rectifier.
> G.


Just a quick update on my own post...
There are tonnes of reviews and "how to" on the net about swapping 6L6 tubes into a Deluxe reverb...
Looks like to new bias for the 6L6 is 32-35 ma.

thats all I got for now....haven't done anything yet BUT its very tempting...
G.


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## guitarman2 (Aug 25, 2006)

I've read some incidences on line of players blowing the OT in their deluxe using 6L6. Some think they'll gain more watts but isn't it limited by the OT?


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## epis (Feb 25, 2012)

guitarman2 said:


> I've read some incidences on line of players blowing the OT in their deluxe using 6L6. Some think they'll gain more watts but isn't it limited by the OT?



Of course, using 6L6s in deluxe is just temporary 

Until you blow fuse or transformer(s)


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## StevieMac (Mar 4, 2006)

Output, with regard to watts at least, will ALWAYS be limited by the OT. If you're OT is good for 25 watts but your tubes are good for 50, you're still only getting 25 watts...max. IIRC, the issue with the OT is an impedance mismatch when you switch from Vs to Ls. That's why Allen amps have a toggle to switch from 8 to 4 ohm when swapping out tube types.


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## GTmaker (Apr 24, 2006)

guitarman2 said:


> I've read some incidences on line of players blowing the OT in their deluxe using 6L6. Some think they'll gain more watts but isn't it limited by the OT?


I read the same incidences about the blown OT BUT there are also plenty of folks saying that they have gone to 6L6 and all is well for years...

As for the speaker impedance going to 4 ohms with 6L6....is that not to ensure more power. ?
All amps offer more watts at lower impedance....correct?


G.


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## nonreverb (Sep 19, 2006)

GTmaker said:


> I read the same incidences about the blown OT BUT there are also plenty of folks saying that they have gone to 6L6 and all is well for years...
> 
> As for the speaker impedance going to 4 ohms with 6L6....is that not to ensure more power. ?
> All amps offer more watts at lower impedance....correct?
> ...


I've had 5881's in my SF Deluxe Reverb for years. Rebiased and that's it. I suggest to anyone doing this NOT to use a solid state rectifier. That will increase the plate voltage causing a bit more plate dissipation on the 6L6's which could stress the output transformer to a point where problems may arise.....as always: The risks are yours to take. I've not had a problem with mine though.


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## guitarman2 (Aug 25, 2006)

GTmaker said:


> I read the same incidences about the blown OT BUT there are also plenty of folks saying that they have gone to 6L6 and all is well for years...
> 
> As for the speaker impedance going to 4 ohms with 6L6....is that not to ensure more power. ?
> All amps offer more watts at lower impedance....correct?
> ...


ah well then the odds are probably low. What are the chances that you'll be one of the unlucky ones? My philosophy is to use my amps as they were designed. I'd rather just buy an amp and use it as intended then try to make it something its not. I know you have 6L6 tubes but its not like 6V6 tubes are expensive.


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## jb welder (Sep 14, 2010)

guitarman2 said:


> I've read some incidences on line of players blowing the OT in their deluxe using 6L6. Some think they'll gain more watts but isn't it limited by the OT?





StevieMac said:


> Output, with regard to watts at least, will ALWAYS be limited by the OT. If you're OT is good for 25 watts but your tubes are good for 50, you're still only getting 25 watts...max.


There is a bit of mixing up in those statements, power is limited by the Power Transformer, not the Output Transformer. The OT will _try _to deliver whatever you put into it, and if you exceed it's wattage rating it will burn up. (example, putting 50W OT in 100W amp)
But in the case of the Deluxe, the output power is limited by the PT, so the 6L6's are not going to put out more power and fry the OT.



GTmaker said:


> As for the speaker impedance going to 4 ohms with 6L6....is that not to ensure more power. ?
> All amps offer more watts at lower impedance....correct?


Using a 4 ohm speaker with the 6L6's would give a better impedance match. With output transformers, you get full power at the proper match, not at the lowest impedance. The Deluxe OT is designed for a pair of 6V6 matched with an 8 ohm speaker. If you change to 6L6, you can balance it out for best match by changing to a 4 ohm speaker. It will still work ok with the 8 ohm, but you may lose a bit of power.
"More watts at lower impedance" is for transistor amps. Transistor amps give most power at lowest impedance (because they don't have output transformers). But with transistor amps, if you go lower than the amp is designed for, they will overheat and fry.


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## GTmaker (Apr 24, 2006)

jb welder said:


> There is a bit of mixing up in those statements, power is limited by the Power Transformer, not the Output Transformer. The OT will _try _to deliver whatever you put into it, and if you exceed it's wattage rating it will burn up. (example, putting 50W OT in 100W amp)
> But in the case of the Deluxe, the output power is limited by the PT, so the 6L6's are not going to put out more power and fry the OT.
> 
> 
> ...


fantastic post on all counts....thanks for taking the time.
G.


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## Jim Jones (Sep 18, 2006)

A friend of mine ran 6L6’s with a plug-in SS rectifier for quite a few years but the power transformer eventually fried. I replaced it with a beefier Hammond which will handle both but I’d stick to 6V6’s if it were mine.


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## GTmaker (Apr 24, 2006)

attention Mr. jb welder and all other interested parties.
I have a question that comes from a complete novice as to amplifiers inner working so please be kind.

the setup...
my recently purchased "used" Deluxe Reverb came with a complete set of GT tubes.
A couple of days ago I decided to check these tubes as I have a nice ancient tube tester that works well.

The GT6V6-s power tubes tested @ about 50 % power....I would think that this was primarily due to the fact that they where biased @ 35 ma
( as far as I know, the 35 ma setting is normal for 6L6 power tubes and is very very hot for 6V6 power tubes.)

What if I installed a set of 6L6 power tubes and biased them @ 30 ma.

Question:

What is more stressful on the Deluxe Reverb RI OT or what ever gets stressed in an amp.?

A set of 6V6 power tubes biased @ 35 ma OR a set of 6L6 power tubes biased @ 30 ma

all hands on deck for this one and please if possible , dont get too technical .
G.


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## Jim Jones (Sep 18, 2006)

The trouble with those bias current numbers is they don’t mean anything without context, i.e. plate voltage. Years ago Ted Weber asked if he could use the chart I posted on my DIY website. I can’t take any credit for it - I just took Randall Aiken’s info at the time and compiled it in a (Geocities caliber!) form. I printed them out and have had them over my bench ever since.

Weber Bias Calculator

Hope this helps!


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## GTmaker (Apr 24, 2006)

Jim Jones said:


> The trouble with those bias current numbers is they don’t mean anything without context, i.e. plate voltage. Years ago Ted Weber asked if he could use the chart I posted on my DIY website. I can’t take any credit for it - I just took Randall Aiken’s info at the time and compiled it in a (Geocities caliber!) form. I printed them out and have had them over my bench ever since.
> 
> Weber Bias Calculator
> 
> Hope this helps!



actually it doesn't help at all....
I understand the idea of plate voltages etc etc.
What I do know is that my Deluxe Reverb has one trim pot to set the bias....so whatever plate voltage is on one tube and whatever plate voltage is on the other tube, I cant do anything about it but use the trim pot to bias both tubes....
And another thing....I would think that a standard Fender Deluxe Reverb RI would produce a plate voltage that is well known to anyone who understands that stuff.
This amp is NOT a custom build that has unknown components that would definitely effect plate voltages.
G.


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## Jim Jones (Sep 18, 2006)

But you have to measure the plate voltage and bias accordingly otherwise you’re going to melt your tubes. Look at the chart.


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## nonreverb (Sep 19, 2006)

Part of my reasoning for using 5881's has more to do with the inherent characteristics of higher power tubes. After years of using Deluxe Reverbs I finally realised that I'm not a huge fan of 6V6 breakup...particularly in that circuit. The 6L6 family of tubes tends to stay more linear in the bass frequencies in that circuit. I also decided not to use a 4 ohm speaker even thought the increases in power isn't major, it still is additive and under certain conditions, might put stress on the OPT.
There is another change that one can do (I haven't done it myself yet). Swapping the drop resistors in the B+ to the values used in the larger Fenders which will give a wee bit more headroom in the preamp...like the DR's big brothers.


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## greco (Jul 15, 2007)

Interesting thread.


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## GTmaker (Apr 24, 2006)

greco said:


> Interesting thread.


it would be a lot more interesting if someone could respond to my question.

_Question:
What is more stressful on the Deluxe Reverb RI OT or what ever gets stressed in an amp.?
A set of 6V6 power tubes biased @ 35 ma OR a set of 6L6 power tubes biased @ 30 ma
_
G.


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## jb welder (Sep 14, 2010)

GTmaker said:


> _Question:
> What is more stressful on the Deluxe Reverb RI OT or what ever gets stressed in an amp.?
> A set of 6V6 power tubes biased @ 35 ma OR a set of 6L6 power tubes biased @ 30 ma
> _
> G.


I don't think either will stress the OT too much. The PT is stressed a little more with 6L6's because they run higher heater current, which is something that I don't think has been mentioned yet. Fender transformers are usually pretty robust, so they can handle it. But in some other amp that is running the PT at close to it's limits, running 6L6 when it's designed for 6V6 could lead to PT overheating and possibly damage due to extra heater current used by 6L6's.

In your case, I think the stressed component would be the 6V6, as 35mA is pretty hot bias for 6V6 at (ballpark) 400V plate. Fender tends to run fairly cool bias, so I'd suggest idle current in the 18mA to 22mA range.
Tube amps are pretty forgiving. In most cases too hot bias will just kill tubes (earlier), not the amp.


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## tomee2 (Feb 27, 2017)

Buy some 6V6s? 

I'm all for using 6L6s or 5881s, but the heater draw is higher, and you'll have to bias them at near the same current as 6V6s to not mess up the power supply voltages in the amp or overheat the OT. Feedback also changes because gain changed, and maybe that's an issue? Not sure..
Maybe Rob Robinette says something on his site about this, he's covered nearly everything there.


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## nonreverb (Sep 19, 2006)

tomee2 said:


> Buy some 6V6s?
> 
> I'm all for using 6L6s or 5881s, but the heater draw is higher, and you'll have to bias them at near the same current as 6V6s to not mess up the power supply voltages in the amp or overheat the OT. Feedback also changes because gain changed, and maybe that's an issue? Not sure..
> Maybe Rob Robinette says something on his site about this, he's covered nearly everything there.


The feedback resistor is the same value in the larger 6L6 drive Fenders...820 ohms as it is in the Deluxe. The power tubes aren't really measured with respect to gain but rather amplification factor. Therefor, in the same circuit with the same plate voltage, similar load and both being beam tetrode tubes, they will work just fine. The significant difference is the 6L6 in that circuit is not being stressed. Bass response is significantly tighter with none of the farty overdirven response of the 6V6. Also as stated by jb welder, the power transformer can absorb the extra heater current without much problem.
As I said, I've had 5881's in my Deluxe Reverb for about 8 years now......no problems at all and sounds superior to 6V6 IMHO.


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## GTmaker (Apr 24, 2006)

nonreverb said:


> The feedback resistor is the same value in the larger 6L6 drive Fenders...820 ohms as it is in the Deluxe. The power tubes aren't really measured with respect to gain but rather amplification factor. Therefor, in the same circuit with the same plate voltage, similar load and both being beam tetrode tubes, they will work just fine. The significant difference is the 6L6 in that circuit is not being stressed. Bass response is significantly tighter with none of the farty overdirven response of the 6V6. Also as stated by jb welder, the power transformer can absorb the extra heater current without much problem.
> As I said, I've had 5881's in my Deluxe Reverb for about 8 years now......no problems at all and sounds superior to 6V6 IMHO.


first of all....great reply as are the others...Im actually learning something which in itself is never easy for me.

Can you share you bias setting for the 5881's on the Deluxe Reverb.

While im at it, its never mentioned so I'll ask. When speaking of the Deluxe Reverb, is there an difference with a Deluxe Reverb Reissue and the non reissue?
G.


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## nonreverb (Sep 19, 2006)

GTmaker said:


> first of all....great reply as are the others...Im actually learning something which in itself is never easy for me.
> 
> Can you share you bias setting for the 5881's on the Deluxe Reverb.
> 
> ...


If it's the '65 reissue, it's the same circuit. The '68 reissue however, has some Fender mod abuse.


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## tomee2 (Feb 27, 2017)

AB763 Mods

Rob Robinette's explanation....


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## loudtubeamps (Feb 2, 2012)

GTmaker said:


> first of all....great reply as are the others...Im actually learning something which in itself is never easy for me.
> 
> Can you share you bias setting for the 5881's on the Deluxe Reverb.




...............................................................................................................
If you are comfortable taking your own( high voltage ) current measurements on an original amp (or not a problem on the reissues with the millivolt test point # 36) then may I suggest for the 5881's ?
Don't get too hung up on an specific number for the ideal bias setting.
The numbers ( milliamp current draw ) are a guideline.
With respect to this amp a current draw of 30 to 35..(I would even go as low as 27 m.a. ) will get you in the ballpark.
Keep in mind, the sweep between 27 and 35 m.a. on the pot will be small .
Adjust the pot to your low and high measurements and mark the positions with a marker or tape on the pot case.
Try setting the bias setting by ear...volume up , pick your low open e and let it hang while slowly adjusting the bias trim pot.
Sweep between the marks and listen for a sweet spot, a low end bloom or slight increase in fulness.
When you think you have found it, check the bias to ensure the tubes and not drawing more than 35 m.a. each +-
I run separate bias trimmers and the sweet spot becomes quite obvious because I am balancing the tubes tonally and not just setting for an ideal operating current draw for the tubes.
Same goes for a phase inverter balance control...the sweet spot is subtle but when you have it and the output tubes balanced tonally and biased, the amp opens up and sounds as good as it should.


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## Greg Ellis (Oct 1, 2007)

loudtubeamps said:


> Same goes for a phase inverter balance control...


That's a new concept for me - what's a phase inverter balance control?

Is there a popular amp that implements this, so I can look at a schematic?


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## Lincoln (Jun 2, 2008)

tomee2 said:


> AB763 Mods
> 
> Rob Robinette's explanation....


incredible amount of information on that site. Thank you for posting


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## tomee2 (Feb 27, 2017)

Lincoln said:


> incredible amount of information on that site. Thank you for posting


Thanks, it's crazy the amount of good solid info that guy has up there. He really should compile it all into a book.


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## Lincoln (Jun 2, 2008)

tomee2 said:


> Thanks, it's crazy the amount of good solid info that guy has up there. He really should compile it all into a book.


I'm going to be busy in there for at least a week!


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## GTmaker (Apr 24, 2006)

Lincoln said:


> I'm going to be busy in there for at least a week!


I think my web browser is broken...
When I visited the site, all the words where in Greek.
Does anyone know where the English version is?
G.


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## loudtubeamps (Feb 2, 2012)

Greg Ellis said:


> That's a new concept for me - what's a phase inverter balance control?
> 
> Is there a popular amp that implements this, so I can look at a schematic?


The schematic shows a 10k pot between the 100k and 110k plate resistors... I've been using a 25k pot (that's what I had on hand).
A 12ax is being used here.
I've played with ax and at's both yielding good results with nice tones.

lots of links to explore >>>>> phase inverter balance control - Google Search


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## Lincoln (Jun 2, 2008)

GTmaker said:


> I think my web browser is broken...
> When I visited the site, all the words where in Greek.
> Does anyone know where the English version is?
> G.


try this one
AB763 Mods

It is a "funny" website, construction speaking......so many paths that don't lead back to where you started. I haven't found a central hub yet.


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## Greg Ellis (Oct 1, 2007)

loudtubeamps said:


> The schematic shows a 10k pot... I've been using 25k's (that's what I had on hand). A 12ax is being used here. I've played with ax and at's both yielding good results with nice tones.


Interesting - so the pot is a voltage divider - feed the B+ to the wiper of the pot, connect the two plates in the phase inverter tube to the end lugs of the pot, and dial it up and down to balance the B+ hitting the two plates.

This would usually be hard wired with fixed resistor values, in most amps. Do you notice a significant benefit from dialing this in precisely?

What kind of power handling do you need in that pot? Is a half-watt enough?


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## jb welder (Sep 14, 2010)

Greg Ellis said:


> Interesting - so the pot is a voltage divider - feed the B+ to the wiper of the pot, connect the two plates in the phase inverter tube to the end lugs of the pot, and dial it up and down to balance the B+ hitting the two plates.
> 
> This would usually be hard wired with fixed resistor values, in most amps.


The fixed resistors are still there (100K & 110K), the pot just allows you to tweak their values a little bit by adding a bit of resistance in series. The idea of balancing may be a bit of an assumption. Sometimes we want to add _asymmetry_ for tonal reasons. At least with guitar amps. For hifi, balancing would probably be the goal. For Dumble I guess it could go either way. Sometimes too much symmetry can make things sterile.
It would be interesting to tweak it by ear, then check on the scope to see if you had made it balanced, or imbalanced.


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## Greg Ellis (Oct 1, 2007)

Bouncing back to one of the OP's questions about swapping tubes...

Does a Deluxe chassis have 2 speaker outs by default? Mine does not, but it's not stock.

Plugging in a second 8 ohm speaker would make a 4 ohm load for the 6L6 tubes, right?

Add an extension cab.

Or would that 'external speaker' jack be wired in a way that made it switch over to a different OT tap when a second speaker was jacked in?


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## nonreverb (Sep 19, 2006)

Greg Ellis said:


> Bouncing back to one of the OP's questions about swapping tubes...
> 
> Does a Deluxe chassis have 2 speaker outs by default? Mine does not, but it's not stock.
> 
> ...


The external speaker jack on a Deluxe or any older Fender amp was just a parallel output. Fender didn't bother with a separate tap on the output transformer.


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## GTmaker (Apr 24, 2006)

Greg Ellis said:


> Bouncing back to one of the OP's questions about swapping tubes...
> Does a Deluxe chassis have 2 speaker outs by default? Mine does not, but it's not stock.
> Plugging in a second 8 ohm speaker would make a 4 ohm load for the 6L6 tubes, right?
> Add an extension cab.
> Or would that 'external speaker' jack be wired in a way that made it switch over to a different OT tap when a second speaker was jacked in?


My Deluxe reverb RI has and extension speaker jack and as far as I know, those jacks are always in parallel.
So adding an 8 ohm extension speaker should give you the desired 4 ohms. From what I have read, I would not add the speaker as I think it would
generate a few more watts from the amp and to me, that's not a good thing with the 6L6 tubes.
Please remember that Im a complete amp novice so take everything I say with a pound of salt.

G.


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## nonreverb (Sep 19, 2006)

jb welder said:


> The fixed resistors are still there (100K & 110K), the pot just allows you to tweak their values a little bit by adding a bit of resistance in series. The idea of balancing may be a bit of an assumption. Sometimes we want to add _asymmetry_ for tonal reasons. At least with guitar amps. For hifi, balancing would probably be the goal. For Dumble I guess it could go either way. Sometimes too much symmetry can make things sterile.
> It would be interesting to tweak it by ear, then check on the scope to see if you had made it balanced, or imbalanced.


Indeed...and when you consider that guitar tube amp output transformers primary windings are rarely if ever perfectly balanced and in some cases can be out by more than 10% from each other, imbalance is inherent in the circuit that can't be tweaked.....one of the reasons why guitar tube amps sound the way they do...


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## loudtubeamps (Feb 2, 2012)

FWIW: I haven't measured or scoped the values of the phase inverter, I go for the audible hump and I'm good with that.
I do not have a background in electronics but I do in audio engineering and to my ears the sweet spot is an alignment of signal phase.
This might be an obvious assumption to someone with more knowledge in electronics.
My output tube dual bias circuit and the hump, sweet spot, call it what you will usually measures a difference of no more than 2 or 3 millamps, very rarely do they draw the same amount.


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## loudtubeamps (Feb 2, 2012)

nonreverb said:


> Part of my reasoning for using 5881's has more to do with the inherent characteristics of higher power tubes. After years of using Deluxe Reverbs I finally realised that I'm not a huge fan of 6V6 breakup...particularly in that circuit. The 6L6 family of tubes tends to stay more linear in the bass frequencies in that circuit. I also decided not to use a 4 ohm speaker even thought the increases in power isn't major, it still is additive and under certain conditions, might put stress on the OPT.
> There is another change that one can do (I haven't done it myself yet). Swapping the drop resistors in the B+ to the values used in the larger Fenders which will give a wee bit more headroom in the preamp...like the DR's big brothers.


Richard, have you played through Pat's silverface Deluxe? It has more headroom than most I've played through.
I popped the hood one morning when I was over to Coe Hill and took B+ measurements. 
Everything in the preamp was running about 20 volts higher than normal, not quite at the point of becoming sterile but most of the mush was gone at breakup volumes.
I don't recall the readings on the output section.


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## loudtubeamps (Feb 2, 2012)

Greg Ellis said:


> Interesting - so the pot is a voltage divider - feed the B+ to the wiper of the pot, connect the two plates in the phase inverter tube to the end lugs of the pot, and dial it up and down to balance the B+ hitting the two plates.
> 
> This would usually be hard wired with fixed resistor values, in most amps. Do you notice a significant benefit from dialing this in precisely?
> 
> What kind of power handling do you need in that pot? Is a half-watt enough?


 Greg: The answer to both questions is yes. Cheers.


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## nonreverb (Sep 19, 2006)

loudtubeamps said:


> Richard, have you played through Pat's silverface Deluxe? It has more headroom than most I've played through.
> I popped the hood one morning when I was over to Coe Hill and took B+ measurements.
> Everything in the preamp was running about 20 volts higher than normal, not quite at the point of becoming sterile but most of the mush was gone at breakup volumes.
> I don't recall the readings on the output section.


I can't recall but it may be running a 5AR4 rectifier which will give some more B+ volts in a '70's Deluxe. Word has it Fender spec'd a small increase in B+ voltage on their power transformers after they went with the 5U4 even though the post AB763 schematics don't indicate it. It's interesting that the schematics post AB763 show the same 330V/33oV and 420V Plate voltage with either the 5U4 or 5AR4 tubes versions which is incorrect. Also, @ 120VAC-125VAC line voltage as opposed to 115VAC of old, there is an increase in the B+ as well.
I'm also using a 5AR4 in my '74 and I believe the increase is somewhere around 20V on the plates.


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## Greg Ellis (Oct 1, 2007)

GTmaker said:


> I would not add the speaker as I think it would generate a few more watts from the amp and to me, that's not a good thing with the 6L6 tubes.


I don't think running two speakers will change your power output. Using two speakers will give you more surface area, move more air, and might produce more volume.

Mostly I was just thinking of a convenient way to drop the load to 4 ohms without changing too much.

If you've already got another 8 ohm speaker kicking around in a cabinet, it just takes a minute to plug it in and see how it sounds.

If not, and you're concerned about getting a more appropriate impedance match, then a single 4 ohm replacement speaker would make some sense. 

I'd be looking for something relatively inefficient, personally. From my experience with a Deluxe, the sort of breakup I want to hear doesn't start to happen until I'm up around 7 on the channel volume, and that is LOUD. It would be nice to able to get into that territory without shaking the windows.


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## jb welder (Sep 14, 2010)

Greg Ellis said:


> I don't think running two speakers will change your power output.


It depends on the OT impedance setting, and the load. If you go from unmatched to matched, the amp will deliver more power. I'm not positive but I think that was the context here.


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## nonreverb (Sep 19, 2006)

GTmaker Don't get too hung up on power output with this mod. To begin with, a tube amp does not behave the same way a SS amp does. A solid state amp is directly coupled to the load. Therefore 100% change in load will result in 100% change in output. That's why it's critical not to halve the rated load on a SS amp. It will try and drive it either to the limit of the power supply or the transistors....the latter usually being the case.
As stated previously, loses in a tube amp are dependent of several factors. That said, the reason for me using 5881 tubes is to enhance the bass response and this mod does that. It's the easiest mod to accomplish this as along with swapping the speaker. Also, the slight increase in output wattage with 5881's will probably negate the power loss with an 8 ohm speaker If you wanted to go with a 4 ohm speaker, you've be ok as you wouldn't be looking at more than about 5 watts based on the limitations of both the power supply and the lower voltages in the preamp/phase inverter circuits. However, replacing the rectifier with a solid state one, increasing the preamp/PI voltages to the same spec as the larger Fender amps and a 4 ohm speaker, might put you into a danger zone. I can't say for sure as I've never attempted it with a scope to see the results.
That said, there are no guarantees. I'm only speaking from my personal experience. I've had no problems with mine using this mod.


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## GTmaker (Apr 24, 2006)

nonreverb said:


> GTmaker Don't get too hung up on power output with this mod. To begin with, a tube amp does not behave the same way a SS amp does. A solid state amp is directly coupled to the load. Therefore 100% change in load will result in 100% change in output. That's why it's critical not to halve the rated load on a SS amp. It will try and drive it either to the limit of the power supply or the transistors....the latter usually being the case.
> As stated previously, loses in a tube amp are dependent of several factors. That said, the reason for me using 5881 tubes is to enhance the bass response and this mod does that. It's the easiest mod to accomplish this as along with swapping the speaker. Also, the slight increase in output wattage with 5881's will probably negate the power loss with an 8 ohm speaker If you wanted to go with a 4 ohm speaker, you've be ok as you wouldn't be looking at more than about 5 watts based on the limitations of both the power supply and the lower voltages in the preamp/phase inverter circuits. However, replacing the rectifier with a solid state one, increasing the preamp/PI voltages to the same spec as the larger Fender amps and a 4 ohm speaker, might put you into a danger zone. I can't say for sure as I've never attempted it with a scope to see the results.
> That said, there are no guarantees. I'm only speaking from my personal experience. I've had no problems with mine using this mod.


Once again I would like to thank all those that are contributing to this thread...I have learned a lot..

I was looking for a power output calculator for tube amps based on speaker total ohms but came across this instead.
I came across this web site that has a very interesting bias calculator.
Hope this helps.
G.
Biasing Tube Amplifier Calculator | Amplified Parts


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## GTmaker (Apr 24, 2006)

Just to conclude on this great thread, I have decided to that the safe route and ordered a new set of 6V6GT power tubes for my Deluxe reverb RI.
Although I have learned a lot from some very interesting posts, I think everyone knows I'm not a techie amp guy.
Going the safe 6V6 GT option seems like its in my safe zone and that makes me fell comfortable.
I actually learned what a phase inverter tube does. 
Although not my option, I was very interested to learn that with the proper biasing, 6L6GT power tubes will work.
I also made good use of my Jackson tube tester. Using the tester I was able to match my preamp tubes so that I used a full set of tubes that where all in the same power ballpark.
I don't know if this made any difference but the amp is dead quiet and sounds great.

Bottom line....my amp sounds great and I have learned some stuff that I didn't know before...

G.


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