budda sd30 series 1- running tubes to hot?

[jamme61]

budda SD30 which is 4 el84 cathode biased. It running 370 plate volts with the tubes running as high as 55ma.each. This seems way to hot for el84's? Thinking of increasing the cathode resistor to get the tubes into the 30ma range. Does that sound about right? I've heard these amps run hot but isn't this to hot? thanks for any feedback.

update doubled the cathode resistor from 50 ohms to 100 ohms. Now I have 34ma at 400 volts Is this OK? amp sounds nice.

[tictac]

At 370V 39mA would be close to 100% plate disspation so yea, 55mA is a bit too much.....

Raising the cathode resistor value is one way to decrease your power tube currernt draw....

TT

[jamme61]

I think this amp is going back. I see some burn marks on the small board that holds the filter caps. Problem is the resistors read 100k on the DVM but the color code on them reads 100 OHMs no schematic screwed

[tictac]

Are there four 100 ohm resistors? 100 ohms is a common screen grid value in some EL84 based amps.....

With current draw like you mentioned maybe a tube or two went south on you?

TT

[Gaz]

100% dissipation is normal for cathode biased amps. Plate voltage is a bit high, but remember the real plate voltage is relative to the cathode, not to ground. What is the screen voltage? If they use a relatively high voltage 'choke' resistor before the screen supply to bring it to a reasonable level, then I don't think the plate voltage would be an issue.

You should draw up a schem

[Phil_S]

I think this amp is going back. I see some burn marks on the small board that holds the filter caps. Problem is the resistors read 100k on the DVM but the color code on them reads 100 OHMs no schematic screwed

This is just weird. Heck, you've already fiddled with the cathode resistor, why not just fix this, too? I think 100K would explain the serious current draw. Once you fix this, you can probably go back to the 50r on the cathode.

[jamme61]

OK I want to keep this amp and appreciate the help. I changed the resistors on the power board to 100ohms which immediately blew the fuse. I mis spoke before-- the resistors color band reads 100 ohms but on my DVM they read 100K so 100K must be right. these two resitors seem to be attached to the two main filter caps on the board- I'm thinking they're there to drain the caps on shut off or just balance the voltage to both caps? in any case where these two 100K resistors are the board is discolored -like its been getting a lot of heat there for a long time (traces underneath are fine? the amp is a 2001. The amp get really hot and there's no fan-- the newer models have a fan. The wrong rec tube was in there too. It's suposed to have a 5U4 rec tube but it had a gz34. The amp sounds a lot better with the 5U4 IMHO. still on the fence with this amp, I paid $900 and it looks like at least $150 worth of tubes and filter caps to replace. Thanks for the help on this if would apreciate any more help on this amp thanks

[Phil_S]

If these are screen grid stoppers...typically the 2nd filter cap feeds the screens...the 100r...one end to the screen, the other end to the 2nd filter cap. So the pair of 100r will be joined at the end where they attach to the 2nd filter cap. Bleeders will strap across the filter cap, one end to the + and the other end to the -.

If you want to fix this, it seems like it is time to employ a more methodical approach. Who knows whether Budda will share a schematic, but you won't know unless you contact them. It is certainly worth trying and it could simplify things a great deal. They might share a layout, too. Ask. You have nothing to lose. http://www.budda.com/resources/index.cfm

[xtian]

On the other hand if those 100? resistors ARE balancing resistors for the first reservoir caps, their value should be 100K or higher, like the Mesa Boogie Mk I schematic I'm looking at has 150K 1W balancing resistors.

Can you show us a photo?

[jamme61]

yea I tried to get the schematic no go the rsistors are going from + to - on the filter caps. I'm bringing the amp back. No schematic needs work I could lose a lot of money which Idon't have. Thanks again to everyone for all the help

[Phil_S]

yea I tried to get the schematic no go the rsistors are going from + to - on the filter caps. I'm bringing the amp back. No schematic needs work I could lose a lot of money which Idon't have. Thanks again to everyone for all the help

Sensible decision. Good for you.
It's a dead issue, but those resistors would be 100K not 100r. It is no wonder the fuse blew. 100r is so low as to make a near short at that spot.