73 Silver face Twin Reverb ?

[gtrplayr1976]

Ok...this first thing I found when I powered up the twin is a bad 12AX7 in V2....this is the second one that has gone bad in that slot. This one is microphonic, the other one failed completely....now to remove the chassis...

[m-fine]

Check the voltages on that tube, cathode resistor values (measured), is the bypass cap leaking even though new?

[gtrplayr1976]

With or without tubes ?

[m-fine]

Both. I would look for a bad resistor or cap powered off. Power on and check volts with no tube, if it looks ok test again with a tube.

[überfuzz]

With tubes! Tubes have internal resistance. You need them connected to get proper readings.

[gtrplayr1976]

OK...I did it without tubes, so I'll put the tubes in ,and make the checks .
Does it usually take awhile for the caps to bleed ? ...I have my meter hooked to one of the leads 'and it's draining really slow..

[überfuzz]

Short answer, yes.

Edit: By the, just to make sure. Always connect the black ground prober to ground while you're poking around with the multimeter. If you want to check voltage between different potentials check them one by one and add/subtract the readings.

[gtrplayr1976]

Short answer, yes.

Edit: By the, just to make sure. Always connect the black ground prober to ground while you're poking around with the multimeter. If you want to check voltage between different potentials check them one by one and add/subtract the readings.

Yeah, I had the ground connected when I was reading voltages . It took so long to drain last night that I just had to wait until this evening to continue.

[überfuzz]

If you want to get real low voltage before you get your hands dirty you use a resistor to drain.

I guess that by now you've heard about the infamous tech using a screwdriver. Not a very nice way, but still ZAPP ZAPP and the caps are drained. Seriously, this is what you can do. Connect a resistor, say 20K, to a wire. one end to ground and one to the cap you want to drain. You'll drain the cap faster than you multimeter, but still not in a way that'll make your legs wobbly or damage your caps. If you like to use the multimeter to read voltages just connect it in series with your little device.

GROUND ----[ 20k ]----[ multimeter ]---- Drain connection

Thinking about it, I usually just read the voltage and if it's in the realms of ok I roll my sleeves up and go.

[gtrplayr1976]

If you want to get real low voltage before you get your hands dirty you use a resistor to drain.

I guess that by now you've heard about the infamous tech using a screwdriver. Not a very nice way, but still ZAPP ZAPP and the caps are drained. Seriously, this is what you can do. Connect a resistor, say 20K, to a wire. one end to ground and one to the cap you want to drain. You'll drain the cap faster than you multimeter, but still not in a way that'll make your legs wobbly or damage your caps. If you like to use the multimeter to read voltages just connect it in series with your little device.

GROUND ----[ 20k ]----[ multimeter ]---- Drain connection

Thinking about it, I usually just read the voltage and if it's in the realms of ok I roll my sleeves up and go.

Yeah , I've heard that before....my problem is I don't like sudden ZAPPS ....I'd rather wait for it to drain...I've got time...and I would like to keep it as long as possible.

[MWJB]

Just unplug the amp from the wall, throw the standby switch in to play mode & put the kettle on for a cup of tea (coffee works nearly as well)...by the time you get back the filter caps will all be drained via the 220K resistors in the main filter totem pole.

This applies to all Twin Reverbs built by Fender, early 60's 6G8/6G8A did not have these resistors, so you can just jumper pin 1 or pin 6 of any preamp tube to ground and wait 30 seconds to drain voltage on these...and any other amp. I leave the jumper in place until I'm ready to test & power up.

[gtrplayr1976]

Just unplug the amp from the wall, throw the standby switch in to play mode & put the kettle on for a cup of tea (coffee works nearly as well)...by the time you get back the filter caps will all be drained via the 220K resistors in the main filter totem pole.

This applies to all Twin Reverbs built by Fender, early 60's 6G8/6G8A did not have these resistors, so you can just jumper pin 1 or pin 6 of any preamp tube to ground and wait 30 seconds to drain voltage on these...and any other amp. I leave the jumper in place until I'm ready to test & power up.

I like the coffee idea....helps me concentrate more too

[überfuzz]

MW is right, but still, why not check voltage before you get going. It's nicer to be surprised by the readings on the multimeter than being surprised by an unpleasant sudden prickly feeling... Just saying.

Now it's time to deliver some readings dude.

[gtrplayr1976]

MW is right, but still, why not check voltage before you get going. It's nicer to be surprised by the readings on the multimeter than being surprised by an unpleasant sudden prickly feeling... Just saying.

Now it's time to deliver some readings dude.

Yep, I agree. I'll get those this evening when I get home.

[gtrplayr1976]

OK...here goes the second try at posting this ....
Starting with V1 I will post the AC then DC voltages , pins 1-9 OK ..I missed a pin since 4&5 are jumpered you'll need to move the numbers up 1 at the heaters

V1 = AC - 0 , 0 , 0 , 3, 0 , 0 ,1.35 , 3
DC - 235 , 0 , 2 , 0 , 236 , 0 , 2 , 0
V2 = AC - 0 , 0 , 0 , 3 , 0 , 0 , 1.35 , 3
DC - 233 , 0 , 2 , 0 , 239 , 0 , 2 , 0
V3 = AC - .10 , .28 , 0 , 3 , 0 , .10, .28 , 3
DC - 435 , 0 , 8 , 0 , 435 , 0 , 8 , 0
V4 = AC - 0 , 0 , 0 , 3 , 0 , 0 , 0 , 3
DC - 238 , 0 , 2 , 0 , 239 , 0 , 2 , 0
V5 = AC - .09, .09 , 0 , 3 , .09 , .09, 0 , 3
DC - 429 , -34 , 0 , 0 , 378 , -34 , 0 , 0
V6 = AC - 0 , 0 , 0 , 3 , 0 , 0 , 0 , 3
DC - 312 , 101, 132 , 0 , 302 , 102 , 132 , 0
Lots of noise when I was poking around on V6. some hum through pins 1,5 and a loud pop then loud hum on pins 2 ,6

V7 -V10 were all pretty consistent...3 VAC on heaters, -44 VDC on pins 1&5 , 435 VDC on pins 3,4 &6 , others were 0VDC

Verdict ?