# Deluxe Reverb Power Transformer



## ampaholic (Sep 19, 2006)

I have owned a 1967 Deluxe Reverb for several years and it is a fantastic amp. When I bought it the power transformer had been replaced with a PT from a reissue DR. I always wondered whether a better quality transformer would squeeze even more tone out so I just replaced it with a new Mercury Magnetics transformer.
My question is about voltages. I checked a few voltages before and after changing the transformer and with the new MM transformer the voltages have increased. Pin 8 of the rectifier tube measured 427 Volts before and 450 Volts after. Pin 1 of the 2nd preamp tube measured 180 before and 192 after. Pin 1 of the reverb driver tube measured 418 volts before and 440 after.
These voltages are now all higher than original Fender schematics would indicate. I'd be interested in your thoughts on whether these increased voltages should be a concern?
Thanks from the Maritimes!


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## Jeff Flowerday (Jan 23, 2006)

The voltages you see on the schematics are from back in the day when the AC at the wall was lower. 117 or less. Now you consistantly see 120.

Take in the MM is exact to spec of the original you'll get higher voltages at the plate.

Now back to your concern, the higher voltage will be a little harder on your tubes that's all.

The higher plate voltage usually makes the amp feel slightly tighter and sound a little brighter. IMO

What I do to get the voltage back to what was speced on the original schematics is run a 5R4 rectifier instead of a 5AR4. NOS 5R4 rectifiers are cheap and reliable as all hell.


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## Wild Bill (May 3, 2006)

Jeff Flowerday said:


> The voltages you see on the schematics are from back in the day when the AC at the wall was lower. 117 or less. Now you consistantly see 120.
> 
> Take in the MM is exact to spec of the original you'll get higher voltages at the plate.
> 
> ...


Oh dear! Might not be a good idea, Jeff!

All tube rectifiers have a max spec on the size of the 1st filter cap they see in the power supply, in the typical cap input circuit. The data sheet usually gives this info.

The 5R4 is unusual in that it specs a max of only 10 mfd. This is way less than the usual 47 mfd or more we see in tube amps.

What happens is that the tube still works, it just takes a beating and has drastically reduced life expectancy.

I'd look at a 5Y3 or a 5U4. The 5Y3 has a bit less current rating and we see them used most often with 20 watt or so amps, like the common Fender pair of 6V6's. 5U4's are seen with 50 and 100 watt amps. They draw an extra amp of heater current but every Fender power trannie seems to handle it just fine. If you're worried you can run the amp for a gig and at the end put your fingers on the power transformer. The old guy's rule of thumb is that you should be able to put your fingers on a trannie for at least 15 seconds before it's too hot to keep at it.

You can also think about putting a 100 ohm to 200 ohm 10 watt resistor in series with the main B+ lead coming from the cathode of the 5AR4. This will drop the B+ 5-10 volts at idle and up to twice that as the amp is cranked, giving more bluesy sag. That's how Copper Capps work!

Just FYI!

:food-smiley-004:


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## nonreverb (Sep 19, 2006)

ampaholic said:


> I have owned a 1967 Deluxe Reverb for several years and it is a fantastic amp. When I bought it the power transformer had been replaced with a PT from a reissue DR. I always wondered whether a better quality transformer would squeeze even more tone out so I just replaced it with a new Mercury Magnetics transformer.
> My question is about voltages. I checked a few voltages before and after changing the transformer and with the new MM transformer the voltages have increased. Pin 8 of the rectifier tube measured 427 Volts before and 450 Volts after. Pin 1 of the 2nd preamp tube measured 180 before and 192 after. Pin 1 of the reverb driver tube measured 418 volts before and 440 after.
> These voltages are now all higher than original Fender schematics would indicate. I'd be interested in your thoughts on whether these increased voltages should be a concern?
> Thanks from the Maritimes!


One other consideration you'll have to take into account is that if your B+ caps are origional, they are probably rated @ 450V and they are probably due for replacement anyway...you may find that they'll need replacing real soon if you apply 25V more on them...


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## Jeff Flowerday (Jan 23, 2006)

Wild Bill said:


> Oh dear! Might not be a good idea, Jeff!
> 
> All tube rectifiers have a max spec on the size of the 1st filter cap they see in the power supply, in the typical cap input circuit. The data sheet usually gives this info.
> 
> ...


Thanks Wild Bill. I already new that. Actually I use the RCA 5R4GYBs (20 uf) and have been for 6 years without one failing. They are $15 per on Ebay so life expectancy isn't a concern.

As per the resister that Bill mentions. I did similar on my 18 watt builds, I use an 82 ohm resister. I like the sag and it helps prolone the life of your EL84s.


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## ampaholic (Sep 19, 2006)

Thanks for the great advice guys. I also checked the bias and power tube plate voltage. At 30ma the plates have over 450 volts on them. Gerald Weber says in his first book that he likes to biad Deluxe Reverbs at 30ma but to make certain that plate voltage does not exceed 425 volts. The only way I can get 425 volts on the plates is to increase bias to nearly 40 ma!
I'm thinking the B+ resistor is the way to go.
PS. caps were completely overhauled with Sprague Atoms about 3 years ago.
Thanks!


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## Adicted to Tubes (Mar 5, 2006)

You don't need to worry so much.Use the 5R4 rectifier tube and be happy.I hate transformers that are made 'on spec'.The wall voltages are no longer at 110v.What a useless idea.
As far as performance from this amp,try biasing at about 21ma and move up from there.Some 6V6's and some Deluxes like less and some like more.your ears are the best indicator there.There is no magic bias level.I had originally bought into the Gerald Weber idea of hot bias,but found it didn't always work.No two Deluxes are the same,especially vintage ones.The output transformers were often different makes!


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## Wild Bill (May 3, 2006)

ampaholic said:


> Thanks for the great advice guys. I also checked the bias and power tube plate voltage. At 30ma the plates have over 450 volts on them. Gerald Weber says in his first book that he likes to biad Deluxe Reverbs at 30ma but to make certain that plate voltage does not exceed 425 volts. The only way I can get 425 volts on the plates is to increase bias to nearly 40 ma!
> I'm thinking the B+ resistor is the way to go.
> PS. caps were completely overhauled with Sprague Atoms about 3 years ago.
> Thanks!


I'd be real careful here! Talking idle current without including plate voltage is like describing the length of a fish with only one arm!:smile:

You can't just arbitrarily say that you can run the idle up and down if you don't understand how the plate voltage is a factor. That's just asking to burn out tubes!

A tube has a plate dissipation rating. This is the max watts of energy that tube can handle in a certain test setup. Plate watts comes from plate voltage times the plate current.

Now the plate current is only constant in a Class A amp. Most guitar amps like the Deluxe Reverb operate in what's called Class AB1. The plate current will vary from the low point of the idling current to the highest peak of the audio signal going through to the speaker. When biasing these amps the convention is that the idle current should be set by the bias control to be no more than 70% of the Pd figure. That's for the warmest sound without stressing tube life. If you want a thinner sound for metal you can go lower but if you go over that 70% figure you're asking to hurt the tubes. 

A 6V6GTA has a plate dissipation rating of 14 watts. Older "GT" versions are rated at 12 watts but that only applies to those using NOS tubes. All 6V6's produced today seem to be "GTA" versions.

So let's say we have a plate voltage of 450 vdc. Divide 14 by 450 and we get 31 ma. or .031 amp. 70% of this figure is 21.7 ma.! Much lower than 30 ma. indeed.

When the idle current is higher the plate voltage will come down a bit. Let's do the math for 425 vdc. 14/425= 32.9 times 70%= 23 ma. Only a little bit more.

If you want to run 30 ma then you're running the tubes at 13.5 w of Pd. That might be ok in a Class A amp 'cuz it operates differently (and also at a much lower plate voltage). Never in Class AB1. 40 ma would be 17 watts! Helluva overload!

You can only run those higher idle currents if the amp runs on much lower plate voltages. The two numbers work hand to hand in the math ratio.

If the tubes are running too hot you'll see pink, red or worse yet white spots on the outer plate sleeve you can see when you look through the glass into the tube. That's your plates trying to melt! 

They're your tubes and you can do what you like but the math is the math. 


:food-smiley-004:


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## ampaholic (Sep 19, 2006)

Thanks for the help! I'm still a bit confused about what to do here though. I certainly don't want to burn out tubes or worse, an output transformer. So I'm all for lowering the bias at idle but that sends my plate voltage, which is already high, through the roof! If I add the B+ resistor will that help control the plate voltage at lower bias levels?
Thanks a lot guys!


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## Adicted to Tubes (Mar 5, 2006)

Yes it will.However,the resistor can get pretty hot.I suggest using the 5V4 rectifier tube.It will lower the voltage to reasonable levels.
If you must use a resistor,get a 25 watt 180 ohm resistor and mount it inside on the chassis so it disipates the heat.Use heat transfer silicone between the resistor and the chassis.It goes after the rectifier from pin 8 to the board.
you MUST keep that resistor well away from other wires and components.
Jeff's suggestion of the 5V4 is way better.Better still,get the proper PT.The mojotone ones have the proper B+.


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## Wild Bill (May 3, 2006)

Adicted to Tubes said:


> Yes it will.However,the resistor can get pretty hot.I suggest using the 5V4 rectifier tube.It will lower the voltage to reasonable levels.
> If you must use a resistor,get a 25 watt 180 ohm resistor and mount it inside on the chassis so it disipates the heat.Use heat transfer silicone between the resistor and the chassis.It goes after the rectifier from pin 8 to the board.
> you MUST keep that resistor well away from other wires and components.
> Jeff's suggestion of the 5V4 is way better.Better still,get the proper PT.The mojotone ones have the proper B+.


Thanks for reminding me about 5V4's, A2T! I've got a few in the junkbox but somehow I never think of them. It's always 5Y3 or 5U4 this and that.

I used to have a great memory before the kids came! It's still 100% but only as long as it lasts...

:food-smiley-004:


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## ampaholic (Sep 19, 2006)

Heh guys, I thought I would give you an update. I actually found a problem in the amp that was likely contributing to my wonky voltages.
When I went to try the 5V4 rectifier as suggested I couldn't get any voltage on the preamp tubes. At first I thought I might have fried the choke however after a bit more troubleshooting I discovered a broken solder joint on the 10k resistor after the last filter cap. I resoldered and it seems like that helped to reduce the voltages I was reading before.
So, here is what I am getting with the 5V4 installed: Rectifier tube output is 424 V. On the plates of the preamp tubes I am getting about 190 V. With the power tubes biased at around 28 ma my plate voltage on the 6V6's is 417 Volts.
If I put the GZ34 back in the rectifier output goes up to about 438V and all the other voltages increase proportionately. Soundwise the amp seems to like the 5V4 although I have a hard time judging with the amp disassembled. Is it just me or do amps always seem to sound better when they are put back together?
Anyway, my take on it is that with the 5V4 rectifer my voltages are almost bang on with vintage specs. So, I think I'm good to go?
Thanks!


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## Adicted to Tubes (Mar 5, 2006)

Sounds good to me.Of course the amp sounds better all put together!I don't think you will find much difference in the sound from those voltage readings.The current however is s big factor on the tone.Try throttling those 6v6's back to about 21ma and see if you like it.


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