ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Re: OK, but...

:

9/23/2003 2:09 AM
Ray Ivers	Re: OK, but... John, I think with a choke-input filter you probably want to put the standby after the filter cap, in the B+ line to the OT and the rest of the stages. Ray

Today

ampage
archive

And now, a word from our sponsors:

9/23/2003 12:53 PM
JWK	??? That surprises me. I would think it would be just the opposite. Then the first cap would have to be rated for 600v or more. What is the reason for not having all the caps separated from the choke? The caps never see high voltage, the rectifier tube is protected from onrush current. Something else I don't know? Thanks again. John

9/23/2003 2:59 PM
Ray Ivers	John, There are many ways to implement standby - lifting the output tube cathodes, shutting off the screen supply, interrupting B+ to output stage only or entire amp, switching the PT HV secondary, etc. etc. By all means go with the one you're most comfortable with. Ray

9/23/2003 5:05 PM
JWK	Thanks! I just thought there was something else I didn't know about. Time to start ordering some parts! John

9/22/2003 4:23 PM
steve conner	Re: input choke - voltage/warm-up question Correct me if I'm wrong- but I thought the GZ34 rectifier tube was designed to warm up very slowly, slower than all the other tubes in your amp, so that this kind of thing wouldn't happen? If it turns out that it _does_ happen, how about putting a transzorb or MOV across your filter cap? Steve C.

9/23/2003 2:21 AM

Steve,

I think you're right about the design intent of a slow warm-up, but the B+ on my Marshall 50-watter w/GZ34 comes up about 5 to 10 seconds before the EL34's conduct (and takes my 500V caps up to about 490 volts

).

Can Tranzorb/MOV's take a lot of 'conduction events' before they fail? I always thought they tended to open up after only a few , but it probably depends on the type, rating, and application; an overrated one would work fine, I bet.

Ray

9/23/2003 9:12 AM

quote:
"Can Tranzorb/MOV's take a lot of 'conduction events' before they fail?"

The kind of currents we are talking about are far smaller than the ~100A spikes these things are rated to handle. So they won't wear out. The only way you might wreck one is by exceeding the power dissipation rating. I think the rating for the 1.5KE**** transzorbs is around 2 watts.

If they have to absorb like 20mA at 450V, though, that's 9 watts

so you would need something like 5 100 volt transzorbs in series. I don't think you can put them in parallel.

Steve C.

Page 2 of 3