Replacing 5U4GB with solid state recitfier in a SF Deluxe Reverb amp - any mod needed?

[slidincharlie (Carlo P)]

Hi.
I would like to replace the stock 5U4GB rectifier with a Weber WS1 solid state rectifier (only-diode, no-sag "copper cap" direct replacement) in my '77 Fender Deluxe Reverb amp. For the music style that I am going to play I guess that a no-sag (tighter? less spongy?) feeling might be good. I can always revert back to the 5U4GB should I not like the WS1.
My question is: besides checking the bias, do I need to change anything, maybe the first two filter caps? I seem to remember reading that more filtering is advised when switching from tube to s.s. rectification.
I attach the SFDR schematic for reference (my amp fits the A1172 schematic, not the A1270)..
Thanks in advance.
--Carlo

[loudthud]

Not a good idea. B+ will go too high for the filter caps and any 6V6s you're likely to find.

[Leo_Gnardo]

I'm sure all the experts will sound off: "SACRILEGE!" For a few of my customers who need such a thing, I've modded Deluxe Reverbs, not by much, with 6L6 / 5881 output tubes. With bias set appropriately, typically around 32 mA. One fellow has three or four of these and they get a workout. He's hauled one up to the 86th floor of the Empire State Building where it's played three times a week over the past three years, if anyone cares to check it out in person. No failures, even with stock transformers and choke. Solid state rectifier, of course. Nothing fancy just 1N4007's. Filter caps are 500V rated. Power ranges northwards of a clean 25 watts. IF you're planning to run 6V6 in your prize, take advice from Jim Kelley who made his signature amps with four 6V6 run close to 500V: use NOS RCA or Sylvania. $$$, oof! In modern times JJ's 6V6 often stand up to higher voltages. Still it's risky to run 6V's all the way up there.

I hope you'll give it a try and maybe even like the results.

[Chuck H]

I like Leo's idea. Put in 6L6's that will be up to the higher B+, make sure the power supply caps are snuffy and bias it up for the new tubes.

[Helmholtz]

Doubled heater current with 6L6s?

[Chuck H]

Doubled heater current with 6L6s?

Yes. And good observation. In my experience the PT will handle it. I've come across a few Deluxe Reverbs and clones made with transformers for a Deluxe Reverb that had 6L6's installed without issue.

[Mars Amp Repair]

Hello folks,
I have an idea for replacing the tube rect with SS diodes with the multi-diodes from a microwave oven, which have a substantial drop. They would provide the necessary drop and could be doubled in series until the desired B+ were achieved, without having to add a high value ballast resistor in series which would of course just add more drop with any increased current demand which results in essentially make the power supply 'soft'. Probably softer than having a rect tube in there. It would just be a senseless endeavor at that point.
I agree that it is a bad idea to just slap one of the SS replacements in there as the B+ will be raised substantially. It is really taking a risk.
As an example, I had a Sunn 200S that a cust replaced the 5AR4 with a SS replacement. It caused the main filter that was rated at 525V to blow its guts out as the new B+ was in excess of 600V. Also, the amp was designed for 110v AC input which further complicated the issue.
Since I hadn't thought of the microwave diodes at that point, I convinced him that it was in his best interest to just use a 5AR4 rect.

I had a bunch of these diodes from when I worked on microwaves, but have never had the occasion to try them.
I'd be very interested if anyone gives this idea a try. See attached. They probably have different ratings for different wattage microwaves, which would probably translate to more diodes in series in the package, but I'm sure there no amp that would exceed the rating.
Thanx, Glen

[slidincharlie (Carlo P)]

It seems that I have to tell the whole story... I omitted it since I wanted to make it simpler.
The amp is now set up with the WS1 s.s. rectifier, two 100uF@375V filter caps in series instead of two 16uF@450V in parallel in the first filtering stage (sorry about the sloppy terminology, I ain't no tech) and two Svetlana 6L6's.biased at 60% MPD with 415V on the plates (measurements taken a few years ago after making this mod).
I have played the amp only a few times since.
Now I wish to take it back to stock conditions with a pair of new JJ 6V6's, but wanted to try a s.s. rectifier.
What changes should I do if I wanted to try a GZ34 rect, blackface style?

[Chuck H]

Now I wish to take it back to stock conditions with a pair of new JJ 6V6's, but wanted to try a s.s. rectifier.
What changes should I do if I wanted to try a GZ34 rect, blackface style?

BF style with the GZ34 should give a loaded voltage between 440V and 450V in my limited experience. I think JJ's will handle this, but only because it's the go to tube for guys that own these amps. I wouldn't count on it.

Changes to make for using 6V6's AND a diode rectifier (WHY?) are limited. You could add a string of zeners to drop voltage for less sag or a series resistance to simulate the voltage drop of a tube rectifier which would result in the same sag. At which point you may as well use the rectifier tube.

If I may ask, why do you want to use a diode rectifier with the 6V6 tubes?

[slidincharlie (Carlo P)]

If I may ask, why do you want to use a diode rectifier with the 6V6 tubes?

Because I expect that less sag (like with a GZ34) or no sag (s.s. rectifier) might sound better, or more suitable to my taste.
According to the AB763 (blakface) schematic the B+ with a GZ34 should be 420V. Why should it be so much higher in my amp?

[Chuck H]

Well maybe it's not? Here in the US we didn't change to 120V until the 80's. Even though most SF schematics say they expect 120V I suspect some transformers must have been made with 115V primaries inadvertently because some SFDRs with the same PT model are higher by a greater margin than I would expect from bias condition alone. That and some regions here have AC receptical voltage that creeps up over 125V regularly. Some SFDR owners report voltages at about 450 even with the 5U4. You might have better circumstances in your country/region.

[Helmholtz]

Don't speculate - measure.

The JJ 6V6S is specified for a plate voltage of 500V and a screen voltage (even more important) of 450V.
https://www.jj-electronic.com/images...s/pdf/6v6s.pdf

[The Dude]

Don't speculate - measure......

^^^^^^That!

[pdf64]

Because I expect that less sag (like with a GZ34) or no sag (s.s. rectifier) might sound better, or more suitable to my taste.
According to the AB763 (blakface) schematic the B+ with a GZ34 should be 420V. Why should it be so much higher in my amp?

The nominal voltages noted on the schematic apply to the particular amp being measured, which would be from pre production or early production.
Over the following 5 years production, things changed. From https://www.thegearpage.net/board/in.../post-38487408

The blackface Deluxe Reverb had at least 3 different power transformers, possibly more (125P23B, 125P23C, 125P23D, 025130). Each had different output voltages.

[Mars Amp Repair]

Does this not seem like a viable solution worth trying?:
I have an idea for replacing the tube rect with SS diodes with the multi-diodes from a microwave oven, which have a substantial drop. They would provide the necessary drop and could be doubled in series until the desired B+ were achieved, without having to add a high value ballast resistor in series which would of course just add more drop with any increased current demand which results in essentially make the power supply 'soft'. Probably softer than having a rect tube in there. It would just be a senseless endeavor at that point.
I agree that it is a bad idea to just slap one of the SS replacements in there as the B+ will be raised substantially. It is really taking a risk.
As an example, I had a Sunn 200S that a cust replaced the 5AR4 with a SS replacement. It caused the main filter that was rated at 525V to blow its guts out as the new B+ was in excess of 600V. Also, the amp was designed for 110v AC input which further complicated the issue.
Since I hadn't thought of the microwave diodes at that point, I convinced him that it was in his best interest to just use a 5AR4 rect.

I had a bunch of these diodes from when I worked on microwaves, but have never had the occasion to try them.
I'd be very interested if anyone gives this idea a try. See attached. They probably have different ratings for different wattage microwaves, which would probably translate to more diodes in series in the package, but I'm sure there no amp that would exceed the rating.
Thanx, Glen