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

ampage archive

Vintage threads from the first ten years

Plate voltage on BFD

:

4/7/2000 12:21 AM

Plate voltage on BFD

Hi Guys, first time poster here, but here goes. I just recapped my blackface deluxe, no reverb. Upgraded the power supply caps and the bias cap and replaced all bypass caps. Installed some nos phillips 6V6's baised around 28-29 ma. the plate voltage is about 439-440volts. A little high I thought. What are the consequences of running at high voltage ? Should I do the zener diode trck, if so where can I get one ? I am running a 5y3 rec tube in place of the gz34 to lower the voltage, sounds really good, nice sag, but of course major lose in volume. Any info would be appreciated.

4/7/2000 12:27 AM
JCS	Hi Guys, just noticed theres another Jim S so I am JCS from now on. Thanks

4/7/2000 2:39 AM

Is that plate current or cathode current. If plate, I'd say it's a bit warm. My BFD puts out about 430 V with a GZ34. I have about 118 V at the wall. I bias it rather hot at 30 mA cathode current. It hasn't blown any tubes yet and it's on at least an hour a day. Anyway I shoot for 11-12 W dissipation on the 6V6s.

I'm mainly surprised that your supply is that high with a 5Y3. The caps are probably rated at 450 or 475 and are certainly seeing peeks above that at startup. Personally, mine's a bedroom amp, so I'm not too concerned about running it hot and seeing voltages close to yours, but I do plan on building one of those "vintage power" devices outlined at geofex.com for a couple of my other amps. Basically, with a 6 or 12 V transformer of sufficient current, you can knock the voltage from the wall down that many volts and be closer to what the amps originally saw in use.

Cheers,
Matt

4/7/2000 8:36 PM
JCS	Thanks for the reply Matt. Yes that was 439 plate volts with the gz34, it runs about 390-400v with the 5y3. I have about 120 volts at the wall. Could you explain how to figure 11-12 watt dissipation on 6v6's. Also was is the main risk of running at 439v, tubes or caps ?

4/7/2000 9:00 PM

Hi JCS: 439Vdc is not unheard of for Deluxe's. I would measure your screen voltage and see if it's higher than your plate voltage. If it is then I would install 1K-2K/2W screen resistors in place of the 470ohm one's (in fact, I would do this anyway!); right on the tube socket.

Right now with 439Vdc on the plates and 28ma's of current per tube your running those 6V6's at they're limit (439*.028A=12.3Watts of dissipation per tube). I would back the current down to about 24ma's and recheck everything. Since you're running good NOS tubes, I wouldn't worry about the voltage too much. If you're really worried, try a 5V4G rectifier and that will bring the voltage down a little, but not as much as a 5Y3. I personally like good 5AR4's.

4/7/2000 10:47 PM
D	I've often wondered about swapping recifiers, but I thought I read somewhere that 5y3's and 5v4's wouldn't stand up to what amps designed around a 5AR4 or 5U4 could dish out. My DR is my main gigging amp, it gets used most weekends, and driven pretty hard. What's the consensus around here?

4/8/2000 2:18 AM

Thanks for the info guys,I think I'll do the res swap and run the gz34, then recheck everything. If I used a zener to drop the voltage I dont think I could run the 5y3 when I want to. Hey D I think you can run a 5y3 in a DR because its a lower powered amp. I don't think you can do it with a SR. Buy the way the 5y3 sounds good for low volume gigs. I had mine cranked about 8-10 on the volume at an open mike blue jam last week.Bass, drums and 2nd guitar. Nice sag and blusie overdrive

Page 1 of 2