Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on October 31, 2022, 11:25:52 pm

Title: Behavior of 807 power tubes
Post by: Leevi on October 31, 2022, 11:25:52 pm

I have  completed a Standel 25L15 clone and am wondering how the 807 power tubes behave.
The power amp has a balance control, which can be used to set the cathode current to balance.During the warm-up time which is long the cathode current varies irregularly and even after longer time period (1h) an adjustment is needed. The tubes are NOS RCA tubes from 50s-60s?Is that typical for those tubes?

The amp sounds great.
/Leevi

Title: Re: Behavior of 807 power tubes
Post by: PRR on November 01, 2022, 12:34:47 am

Let them cook medium-low for a week, then re-check. If they have been idle for many years they will be a little gassy. Warm getters will re-absorb this.

If they are VERY erratic, short the 100k grid-leak resistors to absorb grid current without throwing grid voltage way off.

Last time I had a very ancient 6L6 in hand (and socket) it took 4 days to stop taking large current. In the factory they ran them RED-hot for an hour. but they could tolerate a few deaths.