VVR Circuit Schematic

[wallybob]

I've used the search function here and have not been able to find a posted VVR schematic. Is this something that is readily available?

[UR12]

I've used the search function here and have not been able to find a posted VVR schematic. Is this something that is readily available?

Here ya go

[UR12]

Double post

server error

[wallybob]

Many thanks Dana!

[Structo]

This may help.
http://ampgarage.com/forum/viewtopic.php?p=65052#65052

[wallybob]

Thanks for the info guys. I'm a little hesitant about hanging a pot off the B+ even though it sound like you guys have done it a bunch of times. If you had only two or three levels of voltage reduction (with a switch) what would they be, i.e., 100% & 50%; 100%, 75%, and 30%; etc.?

[UR12]

Thanks for the info guys. I'm a little hesitant about hanging a pot off the B+ even though it sound like you guys have done it a bunch of times. If you had only two or three levels of voltage reduction (with a switch) what would they be, i.e., 100% & 50%; 100%, 75%, and 30%; etc.?

Wally

If you measure the current flow through a 1 meg pot to ground with 500v on it (That is what the pot is rated at by the mfg) you get .5ma .5ma x 500v = .250w or 1/4 watt. So the 1/2 watt pot is only running at 1/2 it's rated power @ it's mfgs rated voltage. Since most TW are running 400v or less there is even more of a safety margin. Now bolt that pot to a grounded metal chassis and put a plastic knob on it to further isolate your human fingers and I really don't know how it could be any safer. I would be more worried about the standby switch shorting out as it has all of the current from the power supply going through it and also has high voltage on it only there is no plastic knob . If you aren't afraid to reach over and flip a standby switch then why would you be worried about the pot? Just my 2 cents

[UR12]

Double post

Server error. Seems like more often than not, when I post I get this debug error thing and then when I go back it has double posted. Anyone else having this problem??

[Tubetwang]

Double post

Server error. Seems like more often than not, when I post I get this debug error thing and then when I go back it has double posted. Anyone else having this problem??

Yuuup!
Only too bad that it does'nt count for a post.
I was told that knobody would take me seriously unless i have at least 1000 posts...

Major Twang
Working hard to build credibility

[Noel Grassy]

Thanks for the circuit schema UR12.

Yes it does the same thing to me but not as frequently lately. Today it's taken a lot longer to post my messages but it hasn't "hung-up".

[FunkyE9th]

I've been using the VVR on a cathode biased amp and have been very happy with it. If I use it on a fixed bias, do I just get one of those dual pots and divide the bias supply with the other pot? I'm assuming the other pot will also have the 100K resistor (i.e. in series with pot and goes to ground) hanging off of it so that the bias supply can drop down to 10%. Is that correct?


Thanks!

-FunkyE9th

[UR12]

I've been using the VVR on a cathode biased amp and have been very happy with it. If I use it on a fixed bias, do I just get one of those dual pots and divide the bias supply with the other pot? I'm assuming the other pot will also have the 100K resistor (i.e. in series with pot and goes to ground) hanging off of it so that the bias supply can drop down to 10%. Is that correct?


Thanks!

-FunkyE9th

There is a little more to it than that. What you propose may or may not work depending on the bias circuit in the particular amp.

[FunkyE9th]

Bummer...I was hoping it was that simple. I guess I gotta look into it some more...Thanks!

[Tubetwang]

[chopstuck]

If putting a VVR on my cathode biased tweed Super clone, can I use it like zener diode for limiting max voltage too? Darn 365-0-365 PT gives me 440 on the plates. My 6V6 Super clone has a 342-0-342 Pt and 400v on the plates. Would you then use a fixed resistor in series with the pot ?