HF-20 Power Supply Problem

[Walter R]

My two HF-20s that I just dusted off after 15 years operated great for 10 hours continuous. Then one of them went mute. Tube pin voltage checks (I have pin test adapters) indicated that there was no plate voltage to V1 and V2, both 12AX7s. The other tubes had plate voltage, but it was about 15% low. My conclusion is that the last two sections of the second filter cap went bad, and are drawing down the other voltages.
The cap in question is a 20-20-10-10 mfd 450v can, I suspect the middle 10 section went bad. I looked at tubesandmore.com and there is a new replacement can for $35. Or I could install two 10 mfd axial electrolytics under the chassis for $6.50 each. I’m inclined to replace the entire can.
Any advice regarding other testing and additional capacitor sources would be appreciated.

 

[Tinkerbelle]

If that is the original multi-cap can it is probably overdue for replacement.

Some like the custom built cans from Hayseed Hamfest. Others re-stuff the original or you could do a mix of multi-cap and some below.

Others to consider are Amplified Parts, JustRadios (2-section)

I have no affiliations to any of these.

 

[triode17]

Did you disconnect all four sections of the can and test the caps for value, leakage and ESR?

 

[Walter R]

Thanks, I decided to replace both filter capacitor cans. I ordered replacements from Amplified Parts.

 

[s-petersen]

Good choice!, as the other sections were very likely to go as well.

 

[Walter R]

Finally got around to repairing the HF-20. The electrolytic cans from Amplified Parts fit perfectly. I had to replace 2 resistors that didn’t survive desoldering. I bought a desoldering iron to help, but it didn’t put out enough heat for the point-to-point wiring and was useless. The amp sounds great now.

 

[primosounds]

Finally got around to repairing the HF-20. The electrolytic cans from Amplified Parts fit perfectly. I had to replace 2 resistors that didn’t survive desoldering. I bought a desoldering iron to help, but it didn’t put out enough heat for the point-to-point wiring and was useless. The amp sounds great now.

Good job. I like to replace the original electrolytics with film caps like Solen or Panasonic DC link. They are quite small and offer a performance upgrade if you are going to have a long term relationship wiht the amp. EICO chassis is usually big enough to allow the various caps to be located underneath.

 

[Tinkerbelle]

Glad to hear this was a success. Time to enjoy the fruits of your labor.

 

[Walter R]

Good job. I like to replace the original electrolytics with film caps like Solen or Panasonic DC link. They are quite small and offer a performance upgrade if you are going to have a long term relationship wiht the amp. EICO chassis is usually big enough to allow the various caps to be located underneath.

I thought about replacing the caps under the chassis, but so many wires and resistors terminate on the electrolytic can terminals that I might have to install a couple new terminal strips. It was enough work to desolder and resolder them all.

 

[primosounds]

I thought about replacing the caps under the chassis, but so many wires and resistors terminate on the electrolytic can terminals that I might have to install a couple new terminal strips. It was enough work to desolder and resolder them all.

Yes, unfortunately, some additional hardware would be required. But i have lots of parts on hand so as much as possible i try to use them up instead getting a new can cap.
When i do do it i always draw myself a diagram with all the connections so i can make sure that the proper values, arrangement, and wiring is correct.