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

[g1]

Going BACK to my original question:
I have turned the amp on with the s.s. rectifier and no power tubes. The B+ is 423VDC. Shouldn't the 500 V-rated filter caps and the JJ 6V6 tubes be in safe operating conditions?

I would think you should be ok. The 423VDC should come down a little with the power tubes installed. Some brands of 6V6 will handle that voltage better than others.

[Chuck H]

I once had a SF Vibro Champ on the bench with 420 ish Vp!!! This is ridiculously high for a single ended circuit. The old RCA 6V6 was hanging in there but I don't suspect the amp was ever turned up much. The owner never used the trem and wanted a distortion "channel" so that was the mod at hand. As usual at the end of the mods and tweaking I gave the amp the crank it up for a while test and the old RCA just couldn't take it. I ended up putting an EH 6V6 in and it did great. This was right before awareness of the Sovtek 5y3 tubes being more like a 5V4 and that could have been partly responsible for the grossly high voltage. My point is that 6V6's are actually really durable tubes. When I see them in the 420 ish range in a push pull circuit I don't even think about it.

[slidincharlie (Carlo P)]

Ok, now I feel better :-) . After all the schematic shows a 420V B+.
I will put the tubes in, let it run for a while and post my readings here.
Thank you.

[Chuck H]

Ok, now I feel better :-) . After all the schematic shows a 420V B+.
I will put the tubes in, let it run for a while and post my readings here.
Thank you.

Doesn't it seem odd that the schematic would say 420V with a tube rectifier and current loading, Yet that's what you're getting with diodes and unloaded??? I'm worried there may be something else going on here or there may be dirt in the testing for reported numbers. Please re check that you are indeed getting 420V with the diode rectifier and no tubes as reported. Is it possible your amp is wired for a 230V primary and you're running it at 220V? Maybe check loaded filament voltage (tubes in) to see if it's in spec. This can be done with the amp in standby so there's no high voltage on the tubes yet.

[Helmholtz]

Is it possible that the Weber "Copper Cap" contains some means (e.g. a zener diode) to lower voltage?
That would be a nice feature.

[Chuck H]

Is it possible that the Weber "Copper Cap" contains some means (e.g. a zener diode) to drop voltage?

Charlie wrote this in the opening post:

I would like to replace the stock 5U4GB rectifier with a Weber WS1 solid state rectifier (only-diode, no-sag "copper cap" direct replacement)

I don't know about this unit but IIRC the "copper cap" tube replacement units were reported to have some kind of voltage compensation. I'll look into it.

[Helmholtz]

With a zener the no-sag claim would still be correct.

[Chuck H]

The read is vague. The only indication is in the header description:



I'll guess that "Limiter" is a Zener circuit. But it's only a guess. Also indicated by this header there won't be any significant voltage drop with loading (installing the tubes). And I expect that will be the case even with the transformer DCR since the voltage probably won't sag below the 420V regulation.

[Iplayloud]

... and the old RCA just couldn't take it.

When you say it couldn't take it, what happened ?

[Helmholtz]

I'll guess that "Limiter" is a Zener circuit. But it's only a guess. Also indicated by this header there won't be any significant voltage drop with loading (installing the tubes). And I expect that will be the case even with the transformer DCR since the voltage probably won't sag below the 420V regulation.

I interpret the Weber claim as no additional sag by the device (as would be caused by a series resistor).
I'm quite sure it does not compensate for the PT sag as there's no easy way to achieve this.

[slidincharlie (Carlo P)]

From the Weber website:
WS1 - 8-pin Copper Cap. Diodes and Limiter only, No Sag. Vdrop: 1V max @ Imax: 1000ma. Also:
The WS1 is (...) built with diodes for rectification and have no sag. This model also has no inrush current limiting.

These are my readings with the WS1 and JJ 6V6S:
mains 222 VAC, heaters 6.08 V, plate voltage 384 V, bias 22 mA on each tube at idle.
The PT is a replacement with a 230 VAC primary that I bought from FnS TubeTechnologies (a Dutch company) several years ago.
Low mains power and low filament voltage could explain my readings?

[Chuck H]

Agree. The way it reads I wondered if they may have used a simple zener regulation circuit. But it's seems unlikely at this high voltage so you're probably right that they mean "no additional sag" caused by the unit itself.

EDIT: And in fact we can see this is the case by Charlie's post above because he has a 36 volt drop at the plates. This has to be transformer DCR.

[Chuck H]

From the Weber website:
WS1 - 8-pin Copper Cap. Diodes and Limiter only, No Sag. Vdrop: 1V max @ Imax: 1000ma. Also:
The WS1 is (...) built with diodes for rectification and have no sag. This model also has no inrush current limiting.

These are my readings with the WS1 and JJ 6V6S:
mains 222 VAC, heaters 6.08 V, plate voltage 384 V, bias 22 mA on each tube at idle.
The PT is a replacement with a 230 VAC primary that I bought from FnS TubeTechnologies (a Dutch company) several years ago.
Low mains power and low filament voltage could explain my readings?

Thank you for running the readings and the good reporting I'd say you're good to go.

[slidincharlie (Carlo P)]

While the amp keeps on running the plate voltage has increased to 400 V, bias current at 23 mA. We're at about 66% MPD, so I feel safe tube-wise.
Should the lower-than-specs B+ (now at 406 V) and heater voltage worry me in any way?

[Chuck H]

No problem with the voltages. The lower plate volts can only help and the heater voltage is fine. It's within spec and in fact there was a thread here some time back where it was speculated that slightly low filament voltage may extend tube life and the fractional difference in tube performance at only slightly lower voltage was insignificant. So I'd say your circumstances are ideal.

More concerning is that your plates increased 20V as the amp warmed up. I don't know why this should happen. It's may be a coincidence and not related to warm up but rather fluctuation in wall ACV. Since you were good about measuring that when you had 384V you could measure again and see. Check plate volts again at the same time to see if there's a correlation.