Recent Posts

71

Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by bmccowan on January 20, 2026, 10:37:59 am »

SEL49 knows Sluckey really well  So I imagine he will jump back in.

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by mountainhick on January 20, 2026, 10:23:14 am »

I am perplexed by Sluckey's "Smoky" running higher screen voltage than the plate. Is there anything with the large choke that would help regulate this?

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Other Topics / Re: Anybody watching Gold?

« Last post by EL34 on January 20, 2026, 10:19:25 am »

The New Banking RuleLooks like Gold is now a tier one asset

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by mountainhick on January 20, 2026, 10:15:33 am »

but I did have one project that ate/redplated tubes at 280 plate volts

Plate voltage alone does not cause red plating. With the proper screen voltage control (you must protect the screens from over dissipation) and bias, they will not red plate. I believe a plate voltage of 280V is not an issue for the 6AQ5 and also that there is room to push the plate voltage even a bit further. All three of the PP amps I posted all run plates over 250V with the U-155R over 300V. IMO, unless you push the voltage so high that the tube arcs, plate voltage above 250V is not a problem.

I'll add that looking over the schematics shared to this thread. there's a marked difference in the versions designed closer to tube spec sheet norms compared to the screaming banshees! And I know for my stash of 6AQ5s how I will approach things.

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by mountainhick on January 20, 2026, 10:06:22 am »

but I did have one project that ate/redplated tubes at 280 plate volts

Plate voltage alone does not cause red plating. With the proper screen voltage control (you must protect the screens from over dissipation) and bias, they will not red plate. I believe a plate voltage of 280V is not an issue for the 6AQ5 and also that there is room to push the plate voltage even a bit further. All three of the PP amps I posted all run plates over 250V with the U-155R over 300V. IMO, unless you push the voltage so high that the tube arcs, plate voltage above 250V is not a problem.

Of course. Revisiting that project I might have upped screen resistor values, and they may have been weak tubes though they tested well on my SECO.

That project though, the old scrounged PT was able to provide 300V B+ to a pair of EL84, so swapped and never looked back.

I also found posts by Geezer here that talked about having to reduce dissipation until he had redplating in control. Seems not an entirely inconsistent problem. I remain impressed by Sluckey's SE version.

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by mountainhick on January 20, 2026, 10:03:43 am »

The other aspect is the option to choose readily available cheaper tube types, but that too has it's own idiosyncrasies.

Yes it does. I have had fun and success with 6973 alternatives 6CM6 and 6CZ5.

I have some 6CM6 and also 6CL6 on deck. Have used 6AK6, 6F3P, 6F4P, 6P1P

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by astronomicum on January 20, 2026, 10:03:00 am »

but I did have one project that ate/redplated tubes at 280 plate volts

Plate voltage alone does not cause red plating. With the proper screen voltage control (you must protect the screens from over dissipation) and bias, they will not red plate. I believe a plate voltage of 280V is not an issue for the 6AQ5 and also that there is room to push the plate voltage even a bit further. All three of the PP amps I posted all run plates over 250V with the U-155R over 300V. IMO, unless you push the voltage so high that the tube arcs, plate voltage above 250V is not a problem.

78

Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by bmccowan on January 20, 2026, 09:59:05 am »

The other aspect is the option to choose readily available cheaper tube types, but that too has it's own idiosyncrasies.

Yes it does. I have had fun and success with 6973 alternatives 6CM6 and 6CZ5.

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Tube Amp Building - Tweaks - Repairs / Re: Favorite 6AQ5 SE and PP power sections?

« Last post by mountainhick on January 20, 2026, 09:46:15 am »

I suspect that "safe" operation does not really equate to tube longevity all that well. Back in the day - carry spare tubes. No crying when a power tube goes. With the price of tubes today it makes sense to either have a lot of amps, so that none get stressed too much, and/or use power tubes within, or close to, their design specs. But then I prefer amps that do not push the power tubes too hard. I may be in the minority there. But 6V6s run at 325 to 350 Vs are sweet.

I do believe that operating within spec promotes longevity, and it remains a serious consideration for me as well. The other aspect is the option to choose readily available cheaper tube types, but that too has it's own idiosyncrasies.

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Tube Amp Building - Tweaks - Repairs / Re: Fender 6G8 hum

« Last post by uki on January 20, 2026, 09:37:12 am »

Probably want to check resistances across your filter caps with the amp off and drained.  Try with the stand by switch open, as that will isolate the reservoir caps from the other caps in the chain.

I've disconnected the + side of the reservoir caps from the circuit and measured uF and  resistances

cap 1 - 21.98uF ,  there is ohms and raising, did read it until 4-5m 
cap 2 - 21.58uF ,  there is ohms and raising, did read it until 4-5m
DMM can read 200m ohms

there was a moment when cap 1 was reading like 160m ohms and raising(confusing), then after reading again it gave the reading above.
DMM battery is new

also i did this test and result seen to be the good case

Also i did a esr test with scope(hope i did this right) follow on pics

Thanks