7236 and 6080WB Power Tubes produce no sound.

[currly30]

I have had the amp for about 6 years now but when I recently tried to swap to a 7236 or 6080WB Power tube the Amp will not produce any sound. It works Fine with a 5998, 6080 and 6AS7G.

Any ideas why the amp is no longer working with 7236/6080WB?

[Paul Birkeland]

Do these tubes glow in the amp?  What are the voltages in the amp with these tubes that aren't passing signals?  Are the plastic keyways on the bottoms in tact?

[currly30]

The tubes glow and the plastic keyways are intact.  I haven't checked the voltages yet since I can't find my manual with what areas to check.

[Paul Birkeland]

You want to measure the DC voltages on terminals 1-10.

[currly30]

Everything tested with in 10%-15% of given numbers with the stock tubes. Before testing testing with the 7236 tube. I decided to use a small nylon brush to clean out the socket and now the 7236 tubes are working and everything test normal. Not sure why It was failing on the 7236 and 6080WB. I'm going to leave the amp on for a couple days to make sure that it keeps working.

I did notice that the ohm check on the left RCA center pin(50) was half the value of the right RCA center pin(100). I can't hear any imbalance on the channels. I did replace the potentiometer a few years ago with a stepped attenuator.

[Paul Birkeland]

Is that 50K vs. 100K?  I think I'd be putting in a different attenuator.

It's possible that the pins are a bit corroded on the tubes that didn't appear to be working.

[currly30]

Yes, that is 50K vs 100k. I was thinking I should get a different attenuator or put back in the original potentiometer.

[currly30]

What level of kOhm resistance do I need a stepped attenuator to be?

[Paul Birkeland]

Either a 50K or a 100K attenuator is a good option.

[currly30]

It turns out the difference in the left right channel on the attenuator is only when it is set to as low as it goes and the first step up. The imbalanced goes away as soon as you go past the first step, within 0.1k volts of balanced. Do you think I should still replace it or is the imbalance okay at low levels?

[Paul Birkeland]

Can you send a link to the attenuator you installed?

[currly30]

I bought it off of eBay a few years ago. It doesn't appear to available anymore.  It was a 24-Step Stereo Attenuator Potentiometer Dale 50k resistor made in China. Kinda like this but the connectors are on the boaad on the bottom. https://www.ebay.com/itm/224611416294?hash=item344be238e6:g:JJ8AAOSw2RVhQqHk

[Deluk]

There is a resistor mod that reduces the signal just a little bit that can be used with the standard pot so it should also be usable with yours. It brings up the volume range to more midway than the first quarter.

[Paul Birkeland]

The resistance from center pin to ground on each RCA jack shouldn't change by much as you move the switch.