66 deluxe reverb - can the original PT run a 5u4?

[Ronno25]

I have a 66 deluxe reverb here and I'm wanting to drop voltage, which is about 450 with a GZ34. Can I safely run a 5u4 that draws 3amps?

PT code 025130

I'm not sure how they were building these blackface deluxe reverb power transformers. I know the silverface ones can run 5u4's and did come stock with them.

 

[Jon Snell]

It depends on the model.
For instance it it is an AB763, it is designed for a GZ34 which is a 1.9Amp draw from the transformer and a 5U4 will cause overheating and eventual failure.
The PR239 has a 5R4 again only a 2Amp draw. The 6G3 is an odd ball and has a lower HT but the heater supply is similar.
I think 3Amps is too high but the replacement transformers come with a 3Amp heater winding.
So to recap, if it is stock it won't handle the current, if it is a replacement, it might/probably will.
The stock mains transformer produces 466 volts DC off load from a 330 - 0 - 330 volt primary. Oddly enough the main smoothers are rated at a mere 450 volts!

 

[Wally]

@Ronno25, a 5V4 drops 15 more volts than does a GZ34 and draws only 2 amps…safe for that PT. A 5R4 drops 50-55 volts more than the GZ34 and as @Jon Snell notes is also safe for that PT.

 

[Jasonpatrick]

They all use the exact same power transformer. Schematics shows this. Silverface or black… same transformer… swap away. 5u4gb or GZzzzzzzzz

 

[Wally]

They all use the exact same power transformer. Schematics shows this. Silverface or black… same transformer… swap away. 5u4gb or GZzzzzzzzz

The model numbers changed in 1966. As I understand it, the specs changed for most of the transformers when Fender went from GZ34s to 5U4 rectifiers. I subscribe to the thought that IF one wanted to run a 5U4 in an amp that is spec’d for a GZ34, one would want to observe the temperature created in the PT with the higher current draw demand On the filament circuit.

 

[Jasonpatrick]

The model numbers changed in 1966. As I understand it, the specs changed for most of the transformers when Fender went from GZ34s to 5U4 rectifiers. I subscribe to the thought that IF one wanted to run a 5U4 in an amp that is spec’d for a GZ34, one would want to observe the temperature created in the PT with the higher current draw demand On the filament circuit.

Did you look at the pics I included? Weird that a company would change specs but not the part number..

 

[schmee]

For a vintage Deluxe, I pretty much subscribe to what Jon Snell and Wally said. But it IS done sucessfully. That doesn't mean you wont be the unlucky guy that blows your PT. You can pull the V1 if you dont use the normal channel, might ease the load a tad.
People even run 6L6's in the BFDR's sucessfully, although it is said you shouldnt.
The Weber Copper Cap is another option. A SS device that simulates the sag of a rectifier tube and lowers the draw on your PT.

I keep using the 5AR4 in mine a lot and only use JJ power tubes. It runs 460 volts and sounds fantastic.
I have used the 5V4 also, cant remember what I have in there right now. I would not use anything but JJ's in it though. Learned that lesson years ago.

 

[schmee]

Did you look at the pics I included? Weird that a company would change specs but not the part number..
If they changed and then back in the day I blew my 1965 transformer in 1968, are you saying that the replacement, even having the exact same part number, would then require me to run a 5u4gb in my 65?
The model number may have changed for the circuit but the transformer didn’t

Nothing 'requires' you to use that rectifier, the tranny is just built to handle the higher load or a lesser load.... like the GZ34.

 

[King Fan]

+1 for the 5V4 suggested by @Wally. (And I didn't know about the 5R4).

I have a 66 deluxe reverb here and I'm wanting to drop voltage, which is about 450 with a GZ34. Can I safely run a 5u4 that draws 3amps?

PT code 025130

I'm not aware of the PTs in these. The original FEIC AB763 schematic (date code C-FD, um, March '64?):

A later FMC AA1172 schematic (1972???) helpfully puts the OP's Fender part number by the 125P23B. And... ran a 5U4:

So did the 125P23B evolve under the same model number? Or was it the same over the years?

 

[Jasonpatrick]

+1 for the 5V4 suggested by @Wally. (And I didn't know about the 5R4).




I'm not aware of the PTs in these. The original FEIC AB763 schematic (date code C-FD, um, March '64?):

View attachment 1042084

A later FMC AA1172 schematic (1972???) helpfully puts the OP's Fender part number by the 125P23B. And... ran a 5U4:

View attachment 1042094

So did the 125P23B evolve under the same model number? Or was it the same over the years?

No it didn’t change. It’s the same transformer..

 

[Jasonpatrick]

Nothing 'requires' you to use that rectifier, the tranny is just built to handle the higher load or a lesser load.... like the GZ34.

It’s the same transformer.. in both amps. They are not built differently. If they were built differently, they would have different part numbers, no? Even replacement vintage transformers are the same for both.

 

[Powdog]

A Weber Copper Cap 5U4 rectifier draws zero current off the 5v winding.

I’ve always used 5V4s to stiffen up voltage drop in amps using a 5Y3.

 

[King Fan]

No it didn’t change. It’s the same transformer..

Dude, sorry, I didn't expand the links in your post 4 -- I wasted time looking 'em up and copying 'em again. Duh.

My question (did the specs change with the same model number) was *mostly* rhetorical -- but Fender and Schumacher did some funky stuff. Let's not even talk about the PR rectifier mystery, which was confused by the goofy AA764 *tube* chart *and* various schematics over the years...

 

[Ronno25]

Great info here guys!

My motivation for wanting to drop voltage is that the amp has some icepick that I do not like at all. I have a blackface deluxe non-reverb that doesn't have any of this icepick. I'm not sure dropping voltage would get rid of it but I want to try. I'll pop a 5v4 in and see. Although I don't think 15volts dropped would be enough to make a difference in this regard.

@Jasonpatrick It seems like there isn't anything definitive to say you're wrong, so you may be right! But I'd be nervous to try this given their isn't consensus about it being okay.

I'm open to other suggestions for getting rid of the icepick as well. I'm aware of the usual suspect, the bright cap on the reverb channel. But the icepick remains with that channel cranked up, which would effectively remove it from the circuit. The normal channel, with no bright cap also sounds icepicky.

Edit: I have played with the bias, swapped output tubes, swapped preamps tubes with no success. I also noticed the PI plate resistor that should be 82k reads at 100k. I tried 82k there and heard no improvement.

 

[schmee]

Great info here guys!

My motivation for wanting to drop voltage is that the amp has some icepick that I do not like at all. I have a blackface deluxe non-reverb that doesn't have any of this icepick. I'm not sure dropping voltage would get rid of it but I want to try. I'll pop a 5v4 in and see. Although I don't think 15volts dropped would be enough to make a difference in this regard.

@Jasonpatrick It seems like there isn't anything definitive to say you're wrong, so you may be right! But I'd be nervous to try this given their isn't consensus about it being okay.

I'm open to other suggestions for getting rid of the icepick as well. I'm aware of the usual suspect, the bright cap on the reverb channel. But the icepick remains with that channel cranked up, which would effectively remove it from the circuit. The normal channel, with no bright cap also sounds icepicky.

Edit: I have played with the bias, swapped output tubes, swapped preamps tubes with no success. I also noticed the PI plate resistor that should be 82k reads at 100k. I tried 82k there and heard no improvement.

Until recently I had both the non rev BFD and the BFDR, both vintage. I kep the BFD and sold the reverb one which I'd used for decades.

The Icepick isn't a rectifier issue. Try the normal channel on your DR, it's very close to the non reverb Deluxe in sound.
Even if you clip the bright cap in a DR reverb channel, the channel is different and brighter due to the added circuitry. The normal channel is thicker sounding like the non rev Deluxe.
But you lose the Reverb....

You can try a different value cap at the phase invertor input. It should have a little .001uf disc cap now, try a .01uf or something in between. It's the cap off pin 2 of the 12AT7 PI tube.

 

[Wally]

Did you look at the pics I included? Weird that a company would change specs but not the part number..

IF you compare the schematic for an AB763 DR and a schematic for a SF DR that came with a 5U4 rectifier, you will see that the B+ voltages are identical….even though a 5U4 drops much more voltage than does a GZ34. That strongly indicates that although the transformer model numbers did not change the specs did. IF those specs did not change when they went to the 5U4 in a BFDR, then the B+ voltage would have been significantly lower than the schematic indicates…420VDC B+ voltage. So, the spec for voltage changed. And….I might th8nk that the specs for the heater filament current draw would have changed as well. ….unless the BF PTs were ‘overbuilt’.
As for a BFDR with a plate voltage of 450vdc, I would want to know two things before I did anything. First, what is the wall voltage? The BF amps were designed for 117VAC at the wall. If one is running the amp with a wall,voltage of 125VAC, that is a bit over 7% increase. Rough guesstimate….that puts another 28-30 volts into the equation. 420+30=450. Rough guess that this happens…..but it seems to work out.
Secondly, I would want to know what the bias numbers are. If the amp is biased in the 60-70% of max plate dissipation range, then the voltage is what it is. However, if the amp is biased at say 40% of MPD, then Biasing to the 60-70% range will lower the plate voltage to a point where I am not afraid to run the amp with good tubes. Hey, JJ 6V6s will handle that. Good NOS will, too. Russian and Chinese tubes may not. They are not built like good NOS American tubes or the JJs are built, and they do not like seeing higher voltages. The screens are weak in that respect. That is why before JJs became available, we would either find NOS or install 6L6s.
Triva question…how did Jim Kelly FACS amps run 485VDC to those four 6V6S? He used good U.S. 6V6 tubes. My greatest seller’s remorse is that I sold my FACS amp in 2002. One of the reasons was the plate voltage vis-a-vis availability of a 6V6 that would stand up in the amp. Yeah, it was in a hardwood cab with cane grille….maybe a $10K amp today.

 

[Wally]

The Icepick isn't a rectifier issue. Try the normal channel on your DR, it's very close to the non reverb Deluxe in sound.
Even if you clip the bright cap in a DR reverb channel, the channel is different and brighter due to the added circuitry. The normal channel is thicker sounding like the non rev Deluxe.
But you lose the Reverb....

You can try a different value cap at the phase invertor input. It should have a little .001uf disc cap now, try a .01uf or something in between. It's the cap off pin 2 of the 12AT7 PI tube.

 

[Ronno25]

@Wally The amp is biased up with USA GE 6v6's to about 65% on one tube and maybe 60% on the other, i'd have to check again to know for sure. That's with the plate being at 450. I'll check the wall voltage.

Edit: wall voltage is 121vac.

 

[Jasonpatrick]

IF you compare the schematic for an AB763 DR and a schematic for a SF DR that came with a 5U4 rectifier, you will see that the B+ voltages are identical….even though a 5U4 drops much more voltage than does a GZ34. That strongly indicates that although the transformer model numbers did not change the specs did. IF those specs did not change when they went to the 5U4 in a BFDR, then the B+ voltage would have been significantly lower than the schematic indicates…420VDC B+ voltage. So, the spec for voltage changed. And….I might th8nk that the specs for the heater filament current draw would have changed as well. ….unless the BF PTs were ‘overbuilt’.
As for a BFDR with a plate voltage of 450vdc, I would want to know two things before I did anything. First, what is the wall voltage? The BF amps were designed for 117VAC at the wall. If one is running the amp with a wall,voltage of 125VAC, that is a bit over 7% increase. Rough guesstimate….that puts another 28-30 volts into the equation. 420+30=450. Rough guess that this happens…..but it seems to work out.
Secondly, I would want to know what the bias numbers are. If the amp is biased in the 60-70% of max plate dissipation range, then the voltage is what it is. However, if the amp is biased at say 40% of MPD, then Biasing to the 60-70% range will lower the plate voltage to a point where I am not afraid to run the amp with good tubes. Hey, JJ 6V6s will handle that. Good NOS will, too. Russian and Chinese tubes may not. They are not built like good NOS American tubes or the JJs are built, and they do not like seeing higher voltages. The screens are weak in that respect. That is why before JJs became available, we would either find NOS or install 6L6s.
Triva question…how did Jim Kelly FACS amps run 485VDC to those four 6V6S? He used good U.S. 6V6 tubes. My greatest seller’s remorse is that I sold my FACS amp in 2002. One of the reasons was the plate voltage vis-a-vis availability of a 6V6 that would stand up in the amp. Yeah, it was in a hardwood cab with cane grille….maybe a $10K amp today.

Gotcha. But following that logic, I hope they send ya the right one with the same part number for the amp you need it for… see, doesn’t make sense. If I take my 1969 deluxe reverb with a gz34 in it with 120v at the wall it’s gonna be high , like 450-60. If I take the same amp through my variac at 117 its spot on 415 ish…Now, if I take the same amp at 120v from the wall with a 5u4 in it, guess what happens.. from a manufacturing stand point, if wall voltages are creeping up, what’s the easiest most cost effective way to change the amp? Redesign a transformer that we have tons of in the warehouse or change a rectifier tube?

 

[Ronno25]

Try the normal channel on your DR, it's very close to the non reverb Deluxe in sound.
Even if you clip the bright cap in a DR reverb channel, the channel is different and brighter due to the added circuitry. The normal channel is thicker sounding like the non rev Deluxe.
But you lose the Reverb....

I compared the non-reverb amp with the reverb amp normal channel again.... and they actually sound very similar. It seems you're spot on here. I think I'll just accept the reverb channel for what it is and let it be a bit bright, icepicky. Turns out they invented this thing called a tone knob on the guitar.