amp problems, sorta off topic, sorry im at my wits end

[johngreene]

Not sure what you mean by the variac being turned on afterwards but I am surprised that the fuse would blow with the output tubes removed. They consume the majority of the current and without them, the fuse shouldn't be getting anywhere close to its limit, unless something is wrong.......

Can you trace through what the standby switch is connected too? none of the schematics on the internet show a standby switch. You don't say what the other output tube is for bias when the standby switch is 'active'. Is its bias current zero? Then (one of) your problem(s) is with the bias of this output tube.

--john

[freak scene]

Not sure what you mean by the variac being turned on afterwards but I am surprised that the fuse would blow with the output tubes removed. They consume the majority of the current and without them, the fuse shouldn't be getting anywhere close to its limit, unless something is wrong.......

Can you trace through what the standby switch is connected too? none of the schematics on the internet show a standby switch. You don't say what the other output tube is for bias when the standby switch is 'active'. Is its bias current zero? Then (one of) your problem(s) is with the bias of this output tube.

--john

the other tube is at zero so its acting correctly.  the standby connects to the 2 5 watt 470ohm power resistors to the power tubes and a 10 watt 5k power resistor that connects to 2 51 k resistors which connect to pins 2 and 5 of the 6sn7.

another note is that the two resistors connecting both of the pin 6's together on the power tubes are 100k, but one of them measures at 40k.  would that be causing all these problems?

my tubes are el34's (actually 6ca7).

[johngreene]

Well, the 10W 5K is a bit of a mystery. It would appear that they screen grid is connected to the same supply as the phase splitter throught the 5K 10W. Seems to be quite different from the EL34 schematic.

It also looks like G3 is connected to ground (same as the cathode). Looks like it was setup to use a 6l6 and you are trying to use it with EL34s. Are pins 1&8 actually connected together as it appears in the pictures?

I'm also a bit concerned that one tube biases differently than the other. There seems to be something not right with the tube that wants to glow red when the standby is switched. It looks like you have a mess on your hands and it would be best to trace it through 1 piece at a time, it's fixable but it is going to take some patience to get it all right.

Both 100Ks should read the same, even if measured in circuit. So that may be a place to start.

--john

[freak scene]

Well, the 10W 5K is a bit of a mystery. It would appear that they screen grid is connected to the same supply as the phase splitter throught the 5K 10W. Seems to be quite different from the EL34 schematic.

It also looks like G3 is connected to ground (same as the cathode). Looks like it was setup to use a 6l6 and you are trying to use it with EL34s. Are pins 1&8 actually connected together as it appears in the pictures?

I'm also a bit concerned that one tube biases differently than the other. There seems to be something not right with the tube that wants to glow red when the standby is switched. It looks like you have a mess on your hands and it would be best to trace it through 1 piece at a time, it's fixable but it is going to take some patience to get it all right.

Both 100Ks should read the same, even if measured in circuit. So that may be a place to start.

--john

un beknownst to me when i origninally got it it was set up for 6l6's, i took it to the same tech that replaced the transformer and he re wired the tube sockets for el34's and didnt charge me (i didnt get charged for the output transformer either since the shop i bought it off of was unaware of the problem). 

here is some voltage readings i got through the bias circuit.



schematic i have of the power section from the garnet book (my amp has reverb though):



better shot of the connections under the 10 watt resistor.

[johngreene]

The power tubes are not wired correctly. The schematic you have is not right either. The link to the power amp section schematic I posted earlier is the correct one (no transformer, 2 47K resistors from the phase splitter (they are 51K on your amp)). The 2 100K resistors should be tied together and connected to G3, They are not. Instead, G3 looks like it is shorted to ground. Pins 1 and 8 look like they are shorted together to me. Pin 8 of both tubes should be connected to the junction of the 2 100Ks which then connect to the bias voltage. The 100Ks are connected to the -33Volts but the pin 8's are not.

At least it looks that way from the pictures.

--john

[freak scene]

The power tubes are not wired correctly. The schematic you have is not right either. The link to the power amp section schematic I posted earlier is the correct one (no transformer, 2 47K resistors from the phase splitter (they are 51K on your amp)). The 2 100K resistors should be tied together and connected to G3, They are not. Instead, G3 looks like it is shorted to ground. Pins 1 and 8 look like they are shorted together to me. Pin 8 of both tubes should be connected to the junction of the 2 100Ks which then connect to the bias voltage. The 100Ks are connected to the -33Volts but the pin 8's are not.

At least it looks that way from the pictures.

--john

the schematic isnt right?  its from the garnet book written by gar gillies.  thats bizarre.

[johngreene]

I'm sure it's correct, just not for your amp.

Your schematic shows a transformer being used for a phase splitter and clearly your amp doesn't have that. If you look at the schematic I posted a link to, all the values, parts and connections match up perfectly. Except there is a ground missing from the bias supply.

--john

[freak scene]

I'm sure it's correct, just not for your amp.

Your schematic shows a transformer being used for a phase splitter and clearly your amp doesn't have that. If you look at the schematic I posted a link to, all the values, parts and connections match up perfectly. Except there is a ground missing from the bias supply.

--john

well damn the luck. 

what about the 6sn7?

[johngreene]

I'm sure it's correct, just not for your amp.

Your schematic shows a transformer being used for a phase splitter and clearly your amp doesn't have that. If you look at the schematic I posted a link to, all the values, parts and connections match up perfectly. Except there is a ground missing from the bias supply.

--john

well damn the luck. 

what about the 6sn7?

The 6sn7 is wired very close to this schematic: http://www.lynx.bc.ca/~jc/SessionManPwr.gif with a couple of exceptions:

1. the two 47K plate resistors in the schematic are 51K in your amp (obviously been replaced, probably not an issue).
2. The 22K, 1W resistor in the schematic is either a 30K or a 2K (can't tell the color very well) in your amp (looks original, so I'd say it is a 30K).
3. The bottom yellow 'brick' cap must be the .047uF and looks to be connected correctly.
4. The brown 'sausage' cap is connected to the grid of the 6sn7 pin 4 and then to the (new) white jumper wire that connects to pin 6 of the upper EL34. This is wrong. The brown 'sausage' cap should be connected from pin4 of the 6sn7 and I see the wire that connects it back to the 30K, 1Watt as it should be. However the wire jumper wire is connected to the wrong place. It should be connected to the yellow 'brick' cap right next to it.
5. The other side of the yellow 'brick' capacitor doesn't look like it is connected to anything. So the new white jumper wire is probably just connected to the wrong lug.

Whew, this is hard to do from pictures!

--john

[freak scene]

I'm sure it's correct, just not for your amp.

Your schematic shows a transformer being used for a phase splitter and clearly your amp doesn't have that. If you look at the schematic I posted a link to, all the values, parts and connections match up perfectly. Except there is a ground missing from the bias supply.

--john

well damn the luck. 

what about the 6sn7?

The 6sn7 is wired very close to this schematic: http://www.lynx.bc.ca/~jc/SessionManPwr.gif with a couple of exceptions:

1. the two 47K plate resistors in the schematic are 51K in your amp (obviously been replaced, probably not an issue).
2. The 22K, 1W resistor in the schematic is either a 30K or a 2K (can't tell the color very well) in your amp (looks original, so I'd say it is a 30K).
3. The bottom yellow 'brick' cap must be the .047uF and looks to be connected correctly.
4. The brown 'sausage' cap is connected to the grid of the 6sn7 pin 4 and then to the (new) white jumper wire that connects to pin 6 of the upper EL34. This is wrong. The brown 'sausage' cap should be connected from pin4 of the 6sn7 and I see the wire that connects it back to the 30K, 1Watt as it should be. However the wire jumper wire is connected to the wrong place. It should be connected to the yellow 'brick' cap right next to it.
5. The other side of the yellow 'brick' capacitor doesn't look like it is connected to anything. So the new white jumper wire is probably just connected to the wrong lug.

Whew, this is hard to do from pictures!

--john

im tracing out the amp in ms paint, when im done with that it should be easier to figure out whats going on.  that way i can make all the changes at once.