70s Ampeg V4B Blows Fuses

[g1]

can you tell me again what measurements youdy like for me to post now that it's working. Can you be specific as to whether vdc/vac and what pin/tube to ground or not.

a) DC voltages, black probe to ground (chassis)
R55, R53, R52, R51, both sides of each resistor
V1, pins 1,3,6,8
V2 pins 1,3,6,8
V3 pins 1,3,6,8
V4 pins 1,3,6,8
V201 pins 2,3,5,6,10,4

b) AC volts, one probe on each of the listed pins
(no probe to ground)
V5 (or any power tube) pins 2 & 7
V4 pins 4 & 9
V3 pins 4 & 9
V2 pins 4 & 9
V1 pins 4 & 9
V201 pins 1 & 12

c) Power tubes - idle current measured with eurotubes bias probe
(DC mA range)
V5
V6
V7
V8

[vintagekiki]

Pulled two bad 5881s when received amp. Using two tested good 5881s, amp powers on. In standby getting a hum and no power or preamp tubes lighting up. When taken out of standby, 6 amp fuse blows. This occurs using variac at about 60v.

You started a topic that has 361 posts.
The rules of good behavior say it is queue to inform the forum, in what condition is V4B.
Have you managed to revive it, or is it sadly waiting for some better times on the dusty shelf.
Thanks.

[ca7922303]

You started a topic that has 361 posts.
The rules of good behavior say it is queue to inform the forum, in what condition is V4B.
Have you managed to revive it, or is it sadly waiting for some better times on the dusty shelf.
Thanks.

I will be able to post the measurements that G1 is asking for asap. Working out of town at moment. Thanks for all the help.

[vintagekiki]

I will be able to post the measurements that G1 is asking for asap. Working out of town at moment.

Good luck.
Impatient we are waiting to seeing you.

[g1]

The rules of good behavior say it is queue to inform the forum, in what condition is V4B.
Have you managed to revive it.

He posted (#354) that it is running and sounds good:

I installed the hum balance pot and that made all the difference on the hum, it's now at normal levels I helieve for this amp( I had a V4 stack in 1875). It sounds great. I really appreciate all the help I got on this. I'm extremely grateful. You guys are top notch and I appreciate the patience you had to have to deal with my lack of experience/knowledge.

The other measurements I asked for are just some double checking to see if there are any other issues.

[vintagekiki]

He posted (#354) that it is running and sounds good:

I didn't notice.
Who would manage when there are more posts in this topic than there are days in a year.

[ca7922303]

a) DC voltages, black probe to ground (chassis)
R55, R53, R52, R51, both sides of each resistor
V1, pins 1,3,6,8
V2 pins 1,3,6,8
V3 pins 1,3,6,8
V4 pins 1,3,6,8
V201 pins 2,3,5,6,10,4

b) AC volts, one probe on each of the listed pins
(no probe to ground)
V5 (or any power tube) pins 2 & 7
V4 pins 4 & 9
V3 pins 4 & 9
V2 pins 4 & 9
V1 pins 4 & 9
V201 pins 1 & 12

c) Power tubes - idle current measured with eurotubes bias probe
(DC mA range)
V5
V6
V7
V8

R55(520/520vdc), R53(-8mv/520vdc), R52(370v/15mv), R51(349/369vdc), V1-1(253v), 3(1.9v), 6(180v), 8(1.4v), V2-1(250v), 3(2.5v), 6(28mv), 8(1.6v). V3-1(350v), 3(82v), 6(218v), 8(2v).V4-1(222v), 3(9.4v), 6(222v), 8(9.4v). V201-2(114v), 3(19v), 4(107v), 5(103v), 6(1.7v), 10(349v).

V5-2&7(6vac), V201-1&12(5.5vac), V1(4&9(5.4vac), V2-4&9(4.7vac), V3-4&9(5.0vac), V4-4&9(5.3vac).

Will post power tubes idle current shortly.

[ca7922303]

a) DC voltages, black probe to ground (chassis)
R55, R53, R52, R51, both sides of each resistor
V1, pins 1,3,6,8
V2 pins 1,3,6,8
V3 pins 1,3,6,8
V4 pins 1,3,6,8
V201 pins 2,3,5,6,10,4

b) AC volts, one probe on each of the listed pins
(no probe to ground)
V5 (or any power tube) pins 2 & 7
V4 pins 4 & 9
V3 pins 4 & 9
V2 pins 4 & 9
V1 pins 4 & 9
V201 pins 1 & 12

c) Power tubes - idle current measured with eurotubes bias probe
(DC mA range)
V5
V6
V7
V8

Power Tubes idle current, set dmm on mA, unable to get any readings. Set dmm on vac all four(4) power tubes read a floating 370vac, dmm on vdc all four read 520 vdc.

[g1]

Power Tubes idle current, set dmm on mA, unable to get any readings.

Check in your meter for blown fuse. The 0.5A 250V fast blow fuse.

[g1]

I didn't notice.
Who would manage when there are more posts in this topic than there are days in a year.

Both these things are mostly due to your false belief; that you have no need to learn the english language to participate on this forum.

[Helmholtz]

Check in your meter for blown fuse. The 0.5A 250V fast blow fuse.

Sorry if I missed something, as I decided not to follow this thread.

But I wonder where the OP connected the meter probes and how he/she could get a 520VDC reading.

[g1]

Sorry if I missed something, as I decided not to follow this thread.

But I wonder where the OP connected the meter probes and how he/she could get a 520VDC reading.

He is using a bias probe that has no resistor and requires a meter on DC current function. I suspect his fuse for that function is blown. I take it he set the meter to read volts after getting no reading on mA range. So at that time measuring DC volts at cathode with cathode disconnected from ground.

[ca7922303]

He is using a bias probe that has no resistor and requires a meter on DC current function. I suspect his fuse for that function is blown. I take it he set the meter to read volts after getting no reading on mA range. So at that time measuring DC volts at cathode with cathode disconnected from ground.

Anything stand out in the readings not with the bias probe. I'm running 3-12ax7s, 1- new 6ac10, 4-used 6l6s?

[ca7922303]

He is using a bias probe that has no resistor and requires a meter on DC current function. I suspect his fuse for that function is blown. I take it he set the meter to read volts after getting no reading on mA range. So at that time measuring DC volts at cathode with cathode disconnected from ground.

Your right about the fuse and what I did to get some readings vac and vdc. I'll find a fuse and post readings with bias probe asap.

[g1]

Anything stand out in the readings not with the bias probe. I'm running 3-12ax7s, 1- new 6ac10, 4-used 6l6s?

Are you one full wall voltage, or variac? 520VDC is a bit low (also 6VAC instead of 6.3V at power tube heaters), but if AC outlet or variac is low, that would explain it.

V3 pin3 is too far off, but probably because 12AX7 instead of 12DW7.

V201 pins 2 & 3 not right. Recheck. Also check resistance of R202,R203,R204

R53(-8mv/520vdc), R52(370v/15mv)
V2-1(250v), 3(2.5v), 6(28mv)

The mV numbers are measurement error, re-do