# Convert a 6Volt battery amp to 120 current.



## Frenchy99 (Oct 15, 2016)

I just acquired an old public address amplifier from the 50s. 

Right off , have a problem since this thing was built to connect to a 6 volt car battery ! 

I have a photocopy of the schematic that I will add but looking for the best solution as to how to connect/convert to plug into a reg 120V wall socket ?

All help would be appreciated.


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## Frenchy99 (Oct 15, 2016)




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## BMW-KTM (Apr 7, 2015)

A 6VDC wall-wart is my first thought.

Learn how much juice it needs (amps/milliamps/whatever), find the right connection and search for an adapter using those criteria.


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## Lincoln (Jun 2, 2008)

"I think"........ there has to be something in there to step up the 6 volts, to around 300 to 400 volts for the tubes to function. I made the mistake of googling "vibrator", that took me down all sorts of paths I didn't intend going. I also learned of something called a "dynamo" which was used on a lot of 6 volt radios to up the voltage. Once upon a time.......even car radios used tubes and were 6 volt powered. 

My thinking is, there should be a point where you can tap into the circuit with 120 volts and completely by-pass all that step up mechanism, whatever it may be.


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## Frenchy99 (Oct 15, 2016)

BMW-KTM said:


> A 6VDC wall-wart is my first thought.
> 
> Learn how much juice it needs (amps/milliamps/whatever), find the right connection and search for an adapter using those criteria.





BMW-KTM said:


> A 6VDC wall-wart is my first thought.
> 
> Learn how much juice it needs (amps/milliamps/whatever), find the right connection and search for an adapter using those criteria.


I was thinking of adding a small power converter inside and adding a reg power cord. The power converters semm to be very cheap but need the right Ma current...


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## jb welder (Sep 14, 2010)

Lincoln said:


> My thinking is, there should be a point where you can tap into the circuit with 120 volts and completely by-pass all that step up mechanism, whatever it may be.


That's what I think too, though it may require a different power transformer.


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## Frenchy99 (Oct 15, 2016)

Lincoln said:


> I made the mistake of googling "vibrator"


   
You`ll have plenty of info on that for certain !!!



Lincoln said:


> My thinking is, there should be a point where you can tap into the circuit with 120 volts and completely by-pass all that step up mechanism, whatever it may be.


I`ll be taking pictures later tonight of the items. Currently making room for these.


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## Frenchy99 (Oct 15, 2016)

jb welder said:


> That's what I think too, though it may require a different power transformer.


Will be posting pics tonight of the interior and the current transformers. Hoping the power transformer might have 115V taps...


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## greco (Jul 15, 2007)

I'm following this thread with much interest.


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## Frenchy99 (Oct 15, 2016)

OK, had time to take a few pics.

Here is the PA in question, its in rough shape and an idiot painted it black...


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## Frenchy99 (Oct 15, 2016)

The first thing to take into consideration, all the transformers are Hammond. Whoever painted the chassis was kind enough to write the numbers on everything...

PT









OT


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## Frenchy99 (Oct 15, 2016)

You can tell its an old one by the tubes !!!



















Here is the 6 volts adapter tube !










and its really a tube !


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## Frenchy99 (Oct 15, 2016)

The inside is a mess... someone played in here and I have no clue as to what was the end goal ! ...










The OT should be easy to decipher ...









Here is were the PT connects. It connects to the 6V tube socket under this silver filter ...

















Looks like I could bypass the 6V tube and set up...

I should maybe write to Hammond with the PT number to verify...


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## dtsaudio (Apr 15, 2009)

Here's link that describes the vibrator.








Vibrator (electronic) - Wikipedia







en.wikipedia.org




You are probably going to have to change the power transformer to one that has a 120V primary. Figuring out the secondary voltages is the challenge. That 8Q7 tube may be an issue as well.


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## Frenchy99 (Oct 15, 2016)

Thanks for the link and info.



dtsaudio said:


> That 8Q7 tube may be an issue as well.


Its a 807 power tube, Hammond made all the transformers for SoundMaster and he made 20,000 amps with these tubes. Replacements should exist ! I hope ! or else this is just good for a full rebuild.


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## Frenchy99 (Oct 15, 2016)

I took better pics of the schematic and adjusted the contrast to make it darker.


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## Frenchy99 (Oct 15, 2016)




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## dtsaudio (Apr 15, 2009)

807 makes a whole lot more sense. 
Pretty basic amp. If you come up with a power supply you might have something.


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## Permanent Waves (Jun 2, 2020)

So I'll speak up from whatever experience I have - please take with a grain of salt. If this device was designed to work on a 6V DC power source from a car battery and draws 6 Amps continuous, the easiest way would be to connect it to a power supply that can supply that 6V DC voltage and 6A current (rather than trying to tap into the circuit using a different power supply and risk blowing something up). However, you should get a power supply rated far more than the 6 amp steady-state required, probably more like 10-20 amps (wall-warts won't cut it, they rarely go above 1-2 amp). I have seen some 6vDC - 10000 mA power supplies on Amazon, they look like power supplies for laptops - that MAY work.

The only part I am weary of (and maybe a tube amplifier expert can shed light on this, like nonreverb) is the power-on current draw when you turn the tube amp on. This was designed to be used with a car battery and car batteries have awesome cold-cranking amps (a short but high current peak when you start your car), so if you connect this to any power supply that cannot supply the peak current when you turn it on (when those big capacitors charge up) then you may blow up the power supply. If this circuit was designed to run to a 6V car battery, you may be better off using it with such a battery, though it may be expensive to find one with enough Ampere/Hours to run the amp for any length of time.


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## Permanent Waves (Jun 2, 2020)

OK, I'm hooked on this thread now, it's been too long since I have done this kind of research. To avoid *highly embarrassing* search results, look for RADIART vibrators: "Until the advent of transistors almost all radios that operated from 6-volt or 12-volt batteries used a vibrator to generate the B+ for the vacuum tubes". So the vibrator provides the B+ plate (anode) voltage - that's the high voltage on the tube. The 6X5GT tube is typically used as a rectifier, so I am assuming the vibrator output is an AC voltage (hence "vibrator") derived from the 6V DC input with step-up voltage from the bulky 126347 transformer?

We need Nonreverb on this thread. Rich, where are you?


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## Frenchy99 (Oct 15, 2016)

Just found a brochure that says the amp needs a 6Volt 6Amp power source...










They are dirt cheap power supply... will order one to try with the amp, will still look at converting it.

The top model, model 700 works with both battery 6volts or 115volts... hum.... need to investigate more...


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## greco (Jul 15, 2007)

@nonreverb ...This approach might alert him to the thread.


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## oldjoat (Apr 4, 2019)

just like in the old days when we switched from 6 to 12 volt car batteries .... center tap a 12V battery to get your 6 volts (or 2 6 volt batteries in series .... use 1 battery or the other to draw from ) 

6 volts fed the heaters , the "vibrator" was nothing more than a step up coil and a set of vibrating points .
( there will be a 60Hz buzz when the unit is working off a battery )


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## Paul Running (Apr 12, 2020)

Yeah, you might not like that buzzing sound from the vibrator...not a reliable power supply, anything with contacts have a short-life cycle by today's standards, especially when operated at higher frequencies.


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## Frenchy99 (Oct 15, 2016)

Here is the schematic of the 700... was wondering how this model worked with both power source.


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## nonreverb (Sep 19, 2006)

greco said:


> @nonreverb ...This approach might alert him to the thread.


As much as I'd like to wade into this conversation, I'm glamping with my wife and enjoying a long dram of 14 year old Glenlivet @ Sandbanks. Therefor I can't see my input would be of much assistance at this time. But thanks for thinkin' of me. ;-P


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## jb welder (Sep 14, 2010)

Frenchy99 said:


> Here is the schematic of the 700... was wondering how this model worked with both power source.


The 700 has a separate 120V primary winding that is switched in when using the 'AC cable'.
The unit you have has only the single primary winding.


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## Frenchy99 (Oct 15, 2016)

jb welder said:


> The 700 has a separate 120V primary winding that is switched in when using the 'AC cable'.
> The unit you have has only the single primary winding.


You think i would be safe with a 6V 6A power adapter on this thing ?


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## dtsaudio (Apr 15, 2009)

Frenchy99 said:


> You think i would be safe with a 6V 6A power adapter on this thing ?


 Safe and operating properly are two different things here. You would need either a 6V AC adapter and bypass the vibrator, or a 6V DC and leave the vibrator there. I'm not sure the former would work, as a vibrator doesn't produce a sine wave (like you get from the AC adapter). It produces a series of short duration spikes (much the old ignition points in a car). Putting a pure AC voltage into it, would produce higher voltage, and probably overheat the transformer. The latter may not work becasue these vibrators produce a spike in the reverse direction as well, and the adapter may not like that. 
As for safety, you still have an un-grounded amplifier with some serious voltage inside, not to mention 60-70 year old parts. This thing could go boom pretty easily.


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## TBayLefty (Jul 21, 2020)

I'm fairly experienced with high power DC applications, and converting from AC to high power DC. Ill take a look at that schematic for you over the weekend. But here's a few things to keep in mind.

While the advertisement says it will run of a car battery, what they mean is you can connect it to a the terminals of the battery for a short period of time, and then you will have to run the car. Probably, the optimum performance is achieved with the car running.

You can probably find a solid state equivalent of that vibrator with no moving parts. May be pricy though.

Do not mess with high power DC applications without safety glasses on, ever. I speak from experience.


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## TBayLefty (Jul 21, 2020)

Ok Ive had a bit of a look. The monkeying around just looks like repairs to me. The input power wires have been replaced probably due to deteriorated insulation. There's no components there that cant be replaced, except maybe the vibrator.

Interestingly it looks like this thing is not polarity sensitive, so it doesn't matter which way you hook it up to the battery. That means it has probably never been blown up, so there's a good chance she will work.

There are all kinds of fairly powerful 6v batteries and chargers on amazon, for those toddler cars. Probably your best bet.


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## Frenchy99 (Oct 15, 2016)

Ok . Thanks for the input.

I guess my best bet would be to replace the power transformer. Need to verify if a single 5881/6L6 power transformer will be the appropriate replacement on here .


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## TBayLefty (Jul 21, 2020)

The way I'm reading this diagram all the heaters run on 6v DC, so you would need a 6v heater supply as well as the 5881/6L6 transformer. 

Also this amp wan't designed to ever be near any grid voltage, or earth grounds. So you will have to be very careful if you attach your new power transformer to the case.


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## player99 (Sep 5, 2019)

Would it not be easiest to use a small battery and a charger? I know you don't want that, but a battery and a charger seems easy.


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## High/Deaf (Aug 19, 2009)

Frenchy99 said:


> Ok . Thanks for the input.
> 
> I guess my best bet would be to replace the power transformer. Need to verify if a single 5881/6L6 power transformer will be the appropriate replacement on here .


With all the stuff you mess with, you may be able to justify one of these --- a variable power supply. Great for trouble-shooting and powering up all sorts of things. 











As was mentioned, you'll need 6A of steady-state current, so I would find something that would source at least 10A, to cover inrush current. Mostly likely, you will only draw 6A steady-state when running the amp flat out.


You could also source two 6 volt batteries, charge them in series with a 12V charger (easy to find) and then run them in parallel for a large current 6V power supply. 

Both of these ideas are much easier than sourcing the correct PT, IMO. But whatever floats yer boat.


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## Frenchy99 (Oct 15, 2016)

High/Deaf said:


> With all the stuff you mess with, you may be able to justify one of these --- a variable power supply. Great for trouble-shooting and powering up all sorts of things.
> 
> View attachment 328475
> 
> ...


I do have a Variac that i use to test and charge up new caps after repairs and cap jobs. I would prefer just making this amp plug and play. My variac is 16 lbs. A pain to cary.


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## High/Deaf (Aug 19, 2009)

Frenchy99 said:


> I do have a Variac that i use to test and charge up new caps after repairs and cap jobs. I would prefer just making this amp plug and play. My variac is 16 lbs. A pain to cary.


A variac is AC-to-AC so won't necessarily work without some mods to the amp. You need 6V DC, which requires a DC power supply / rectifier. And for audio work, probably good filtering on the DC side so you don't induce noise in the form of power supply ripple. 

As I said, expensive and probably not worth it for this one project. If you had other uses for it, it may be worth it.


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## Frenchy99 (Oct 15, 2016)

High/Deaf said:


> A variac is AC-to-AC so won't necessarily work without some mods to the amp. You need 6V DC, which requires a DC power supply / rectifier. And for audio work, probably good filtering on the DC side so you don't induce noise in the form of power supply ripple.
> 
> As I said, expensive and probably not worth it for this one project. If you had other uses for it, it may be worth it.


Thank you for all the detailed information. Big learning curve for me. 

At this point im real happy that the amp was given to me.


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## tomee2 (Feb 27, 2017)

What a headache! Just ship it to me and I'll dispose of it for you....and you can go back to your other amps.


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## jb welder (Sep 14, 2010)

High/Deaf said:


> As was mentioned, you'll need 6A of steady-state current, so I would find something that would source at least 10A, to cover inrush current. Mostly likely, you will only draw 6A steady-state when running the amp flat out.


I tend to agree, as it's single ended, so consumption should be the same whether idle or full power output. However, they do show a 15A fuse, so they must be expecting a pretty big surge at turn on?


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## Frenchy99 (Oct 15, 2016)

tomee2 said:


> What a headache! Just ship it to me and I'll dispose of it for you....and you can go back to your other amps.


I would not dare give my headache to someone else !!! 

Would not want to inconvenience you ...


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## Frenchy99 (Oct 15, 2016)

High/Deaf said:


> With all the stuff you mess with, you may be able to justify one of these --- a variable power supply. Great for trouble-shooting and powering up all sorts of things.
> 
> View attachment 328475
> 
> ...



Would this be sufficient ?









DC Power Supply Variable,0-30 V / 0-10 A LW-K3010D Adjustable Switching Regulated Power Supply Digital,with Alligator Leads US Power Cord Used for Spectrophotometer and lab Equipment Repair: Amazon.com: Industrial & Scientific


DC Power Supply Variable,0-30 V / 0-10 A LW-K3010D Adjustable Switching Regulated Power Supply Digital,with Alligator Leads US Power Cord Used for Spectrophotometer and lab Equipment Repair: Amazon.com: Industrial & Scientific



www.amazon.com


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## TBayLefty (Jul 21, 2020)

15A fuse @ 25V = 375 W so @ 6V you could potentially have current as high as 60A, momentarily.





__





Unique Tube Heater Supply






www.tronola.com





Tube heaters have very low resistance when cold, drawing considerable starting current. Some quick measurements and calculations showed that the tube compliment of the ST-35 initially draws 26 amps at 6.3 volts. After warm-up, these same heaters draw 3.64 amps or 23 watts.


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## High/Deaf (Aug 19, 2009)

Frenchy99 said:


> Would this be sufficient ?
> 
> 
> 
> ...


According to the specs, yes, it should be sufficient. 

It's really hard to say how much inrush current the amp will require, but with a supply like that you can manually ramp up the inrush current with the front panel control (making start up take a bit of time instead of being instantaneous - and much like people do with a variac and old amps). You'll also get an idea of how much current (power) it's consuming with the metering.


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## jb welder (Sep 14, 2010)

TBayLefty said:


> 15A fuse @ 25V = 375 W so @ 6V you could potentially have current as high as 60A, momentarily.


I'm not sure where you got the 25V from, unless you mean the safety rating of the fuse. That is not the applied voltage.
6V at 15A is 90W, so that is the max. it can draw then the fuse will blow.
The model plate says 6A so that is probably the steady state draw, 6V at 6A is 36W.
So it seems the amp will draw approx. 36W with possible turn on surge as high as 90W. All at 6VDC.
As @High/Deaf stated, if you bring up the unit slowly on that variable supply, you should have no problem powering the unit.


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## nonreverb (Sep 19, 2006)

I wouldn't waste my time with the 6V circuit. I'd replace it with a proper 120V power transformer. Although if you're unfamiliar with what that involves, might be easier for you to find a large 6v transformer and a 25 amp bridge rectifier and significant filter caps.. Pinball transformer would work great! As for 807's, I have several NOS ones.


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## Frenchy99 (Oct 15, 2016)

nonreverb said:


> I wouldn't waste my time with the 6V circuit. I'd replace it with a proper 120V power transformer. Although if you're unfamiliar with what that involves, might be easier for you to find a large 6v transformer and a 25 amp bridge rectifier and significant filter caps.. Pinball transformer would work great! As for 807's, I have several NOS ones.


I just ordered the DC power supply unit! 

If you can help me determine which Hammond PT I would need, would rather go that route. The 700 model takes both voltage so can use the schematic to follow the mods to make. Same rectifier tube on both 600 and 700 ...


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## nonreverb (Sep 19, 2006)

I could do that or we could work something out for this instead. The better version. Needs to be restored and I have no interest in doing so.
As stated earlier, Hy Bloom made literally 1000's of tube amps in the '50's and '60's here. I knew him and had some interesting conversations with him over the years. He made quality stuff for sure. This is the higher wattage version using 2 807's and more importantly, 120VAC supply.


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## Frenchy99 (Oct 15, 2016)

nonreverb said:


> I could do that or we could work something out for this instead. The better version. Needs to be restored and I have no interest in doing so.
> As stated earlier, Hy Bloom made literally 1000's of tube amps in the '50's and '60's here. I knew him and had some interesting conversations with him over the years. He made quality stuff for sure. This is the higher wattage version using 2 807's and more importantly, 120VAC supply.
> View attachment 328885
> View attachment 328887


PM...


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## TBayLefty (Jul 21, 2020)

jb welder said:


> I'm not sure where you got the 25V from, unless you mean the safety rating of the fuse. That is not the applied voltage.
> 6V at 15A is 90W, so that is the max. it can draw then the fuse will blow.
> The model plate says 6A so that is probably the steady state draw, 6V at 6A is 36W.
> So it seems the amp will draw approx. 36W with possible turn on surge as high as 90W. All at 6VDC.
> As @High/Deaf stated, if you bring up the unit slowly on that variable supply, you should have no problem powering the unit.


I got it from the schematic diagram. I see what you mean, 375w is the interrupt rating. So it's likely the current will be much lower. We use breakers.

You have to excuse me, I've seen some pretty gnarly accidents in high power DC. Molten metal flashes, exploding batteries. I guess unlikely at this low power, but it pays to stay alert.


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## alwaysflat (Feb 14, 2016)

Considerations for your 600 Model power supply replacement, for 6.3vac you need to supply 300, 600 and 900 ma for the 3 tubes respectively ~ so 3.0 Amp or greater secondary 6.3v should be good. Specially if you drop the 6X5 out of the picture with SS rectifier. 
Your DC 435 v, will need a 435* .707 or 307 volt secondary for bridge rectifier, or 435 * 1.414 for a FW rectifier ( call it 615. suggesting 600-0-600 would be fine. If you can find out your B+ power draw or specs from the original PT ( secondary current max ), will help.


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## epis (Feb 25, 2012)

Your math is wrong man. 435 V divided by 1.414 gives you around 300 V.
So, transformer 300 - 0 - 300 would be perfect.


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## alwaysflat (Feb 14, 2016)

epis said:


> Your math is wrong man. 435 V divided by 1.414 gives you around 300 V.
> So, transformer 300 - 0 - 300 would be perfect.


Thanks , What I said , 307 volts. I think I got carried away stating 600-0-600 term ( agree that's wrong) , should be stated as 600 ct .( thanks my bad ) Nothing wrong with my math tho I think . 
x.707 is same as /(root 2)


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## Frenchy99 (Oct 15, 2016)

Just want to thank @nonreverb for selling me his amp! He took the time to pack and ship this heavy thing that was awkward to ship.

Thank you !


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## nonreverb (Sep 19, 2006)

You are most welcome Pierre! It won't take too much to get it going.


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## loudtubeamps (Feb 2, 2012)

nonreverb said:


> You are most welcome Pierre! It won't take too much to get it going.


Wow, looks very clean, love the colour matching end bells, classy.
good on ya'.....


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## Frenchy99 (Oct 15, 2016)

I know its not something technical but just had to express myself towards something that I find super weird...

I like having all the parts needed to restore an amp before undertaking the work, hate having an amp on my bench for 2 weeks.

When I received the amp that @nonreverb so generously sold me, made a list of items and purchase what I thought I might need which brings me to my point.

Seeing that the power tubes were mismatched, I ordered 2 sets of NOS 6P7S / G-807 / G807 tubes from Mother Russia

These:



















What I find so weird is how come I can buy 4 of these and have them shipped to me directly to my door for Total cost of $14 Can !!!    Plus it only took 1 month to get here !!! Took 2 months for my last order from Lee Valley`s ... 

Just the shipping cost here to send to someone in town would cost more and that's without the cost of the tubes !!!

Do we pay to much in Canada for certain services ?... 

Rant over...


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## Paul Running (Apr 12, 2020)

We pay too much for certain things...this is one of them.


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## Paul Running (Apr 12, 2020)

Nice amp...lots of potential there.


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## Frenchy99 (Oct 15, 2016)

Paul Running said:


> Nice amp...lots of potential there.


Yep, cant wait to get her up and running.


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## Paul Running (Apr 12, 2020)

If that's a Hy Bloom design, it will operate forever and a day, he stays well within the boundaries of physics so, it is a virtual fail-safe tube amp, in my eyes.


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## Frenchy99 (Oct 15, 2016)

Paul Running said:


> If that's a Hy Bloom design, it will operate forever and a day, he stays well within the boundaries of physics so, it is a virtual fail-safe tube amp, in my eyes.



Yep, a HY Bloom amp.

Fell in love with these after I got my first one last year, the 050 model.


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## tomee2 (Feb 27, 2017)

Very cool. You have a small collection of these now. 


The 807 thing.... these were made in huge numbers during WW2, then even after kept in spares storage. The home hifi and guitar world didn't use these tubes (except in a few home built hifi amp plans, like the Williamson amp, or a few commercial amps) so the demand in vintage hifi or guitar amps is pretty much nil. 
I dont think any manufacturer today would sell an amp with user serviceable tubes with a HV lead on the top! So, I suspect cheap they will remain for a long time.


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