Bad reverb transformer? maybe the tank?

[KimboDb]

Amp(ab763 SR) is up and running again. no reverb. i tested pin 1 on the 12at7 and got voltage but there is no signal coming from the reverb signal send. i also swapped the 12at7 from the tremolo to the reverb. i pulled the power tubes and turned on the power and from standby to on an no signal whatsoever. i would say the recovery is working cause i still get noise if i tap the tank. Could the reverb transformer went bad but still put out voltage but no signal. also when i swapped the tank into my fender super 112 the new tank doesn't work in my super 112. but the small super 112 tank still works as intended on the super 112. I'm left to think its probably both the reverb transformer, also maybe the tank (3 spring long tank). i double and triple checked my wiring and everything looks ok. the tank does gives me 221ohm on the out side and 1.4 on the in side. 

[tubenit]

Not likely to be the reverb transformer.

My first guess is that something may be  wrong with the reverb tank. Sometimes those small wires on the input end of the tank will break.

2nd guess is that something is not wired correctly.  Also check to make sure the cables to the reverb tank don't have a short or a short to ground.

With respect, Tubenit

[Blind Lemon]

My thoughs are if you get reverb when you tap the tank, swap the in/out cables and see if you still get the reverb. If you do cables are probably good and the output side of the circuit is good. At least you have cut the circuit in half.


BL

[sluckey]

Just a couple notes... There should not be a 12AT7 in the tremolo circuit. Maybe you meant you swapped 12AT7s with the phase inverter?

The reverb tank for the AB763 is not compatible with the Super 112 amp. The reverb tank in the Super 112 is not compatible with the AB763 amp.

How did you resolve the burnt 100Ω resistor problem?

[KimboDb]

Yes. Swapped the phase inverter 12at7. I've swapped the cable ends used different cables and still nothing. The 100 ohm heater resistors burnt, I put new ones in and rewired the heater sockets. I still dont understand why there is no signal being sent from the reverb signal send.

[sluckey]

Could be several things including a wiring error. Measure the voltages on pins 1, 2, 3, 6, 7, and 8 of the reverb driver. We may get a clue from the voltage readings.

[sluckey]

I just looked at the two board pics you posted in other threads. There is a 1M resistor missing from the board and it happens to be the grid resistor for the reverb driver tube. You won't have any reverb without that resistor.

Maybe you could post some updated pics of the entire amp. And maybe keep all posts about this amp in a single thread so we can maintain some continuity. Starting a new thread every time you discover another problem keeps us from seeing the big picture. When you find the fix for a particular problem let us know please.

[KimboDb]

Ok. I added a dwell pot. So I have to still have the 1m resistor? I though that part gets replace by the dwell pot. Ill get some pics up and some voltage readings

[sluckey]

You don't need the resistor

[KimboDb]

Just as a note, dwell and mix are after the volume pot. Tube reading
1 360
2 62
3 62
6 360
7 62
8 62

[sluckey]

Recheck those voltages! If they are still the same then rewire that socket correctly.

[KimboDb]

Ok. Ill check again, was rushing out the house. What should they be?

[sluckey]

Pins 2 and 7 should be zero. Pins 3 and 8 should be approx. 8VDC.

[KimboDb]

Ok pins 3 and 8 are 8v but pin 2 n 7 read -280 that pins 1n7 read -.871, I check it after replacing both v2 and v3 tube sockets and wiring. also i think the tank is good because i did the crash test and got the crash and both inputs from the tank. also still no signal coming from the green wire (reverb send to tank input) of the reverb transformer. i double and triple check the wiring. only the reverb doesn't work. tone stack works as intended. tremolo seems weak but it does work, but i have to go high on the intensity.

[sluckey]

Ok pins 3 and 8 are 8v but pin 2 n 7 read -280 that pins 1n7 read -.871

You keep mixing up the pins. 

Pins 1 and 6 should be connected together.
Pins 2 and 7 should be connected together.
Pins 3 and 8 should be connected together.

You say "pin 2 n 7 read -280". I think you are misreading your meter. That can't possibly be -280 volts. Surely it's really -280 millivolts (which is really close to zero volts).

You also say "that pins 1n7 read -.871". Surely pin 1 and pin 7 are not connected together! Pin 1 and pin 6 should read several hundred volts. You recently said it was 360V.

Please look closely at your meter when measuring volts. Not just the numbers. If the display shows mV please tell us because it's important. And try to be accurate when you actually post the voltages. Don't mix up the pin numbers.

So, check those voltages again.

Also, here's a little test you can do... Connect a speaker to the reverb send jack. You should be able to hear your guitar through that speaker if you turn the dwell pot up. If so, then the reverb driver tube and reverb transformer are working properly.

[KimboDb]

Ok sorry. Oh 1n7 was a typo, I meant 1n6. The meter has an auto feature and it did say mv. Those pins are wired together like the schematic. I did the speaker test and no signal. I did the same test on my super 112 and got signal. It's gotta be the transformer then. Thanks for the help Mr. Sluckey!
When reading the meter I didn't know the whole number was in mv. I thought the number past the decimal point was the mv and the numbers b4 the decimal were the volts like 12.7mv was 12v and .7mv. Lessen learned. I already ordered a new RT and cables. so heres what my meter shows for pins 1 n 6

[sluckey]

With the power turned off measure the resistance between the red and blue wires of the reverb transformer.

[KimboDb]

reading 0.f at the connections to the amp but after i removed if from the chassis between 450k-510k ohm rising and dropping but only if i remove the clip attachments to my multi meter leads. no continuity with the red and blue wire also. black and green read 1.1 ohm and have continuity.

[PRR]

Just to be sure: short the Black and Green, measure that Blu-Red again.

I have seen digital meters be confused by high inductance transformers. I think the measuring time is too quick. Shorting another reading kills 99% of the inductance and gives a decent reading.

We expect a few K Ohms. 500K is wrong. Much under 1K is wrong.

[KimboDb]

with the black and green shorted i get .900 up to 2.200 m ohms. it doesn't stay steady, it goes up and down, up and down.

[PRR]

Smells like bad winding. (The varying reading may be moisture in the winding.)

[2deaf]

Sounds like an open primary and he is touching the business end of the probes with his fingers.

[KimboDb]

ok and yea i was touching the ends, with just using the lead attachments i was getting no reading whatsoever but with the sharp lead i would.

So most likely there was a short on the tube wiring and thats what made the transformer blow? i know when i first put it together i missed 1 wire which goes from the ground to the 22/50v+4.7k resistor. the amp was really loud till i put that wire on. Just want to make sure so iit doesn't happen again.

[2deaf]

So most likely there was a short on the tube wiring and thats what made the transformer blow? . . .  Just want to make sure so it doesn't happen again.

I wonder if the path for the current that burned the heater resistors went through the reverb transformer primary winding.

[shooter]

yea i was touching the ends

You'll probably learn NOT to do that

[KimboDb]

Well i put in the new transformer. Wah La, working like a charm. Im guessing that either it was a short in the preamp tubes v2 or v3 or the fact that i missed one of the wire to ground in the middle of the board on assembly. It had a whole lotta volume b4 i added that wire. sounds really good. reverb is perfect on all setting and the dwell control is awesome. now to decide wether to put it in a head or a custom cab with some good speakers. 
Thank you everyone who gave tips and advise, its greatly appreciated.

[jaquijano]

Ok pins 3 and 8 are 8v but pin 2 n 7 read -280 that pins 1n7 read -.871

You keep mixing up the pins. 

Pins 1 and 6 should be connected together.
Pins 2 and 7 should be connected together.
Pins 3 and 8 should be connected together.

You say "pin 2 n 7 read -280". I think you are misreading your meter. That can't possibly be -280 volts. Surely it's really -280 millivolts (which is really close to zero volts).

You also say "that pins 1n7 read -.871". Surely pin 1 and pin 7 are not connected together! Pin 1 and pin 6 should read several hundred volts. You recently said it was 360V.

Please look closely at your meter when measuring volts. Not just the numbers. If the display shows mV please tell us because it's important. And try to be accurate when you actually post the voltages. Don't mix up the pin numbers.

So, check those voltages again.

Also, here's a little test you can do... Connect a speaker to the reverb send jack. You should be able to hear your guitar through that speaker if you turn the dwell pot up. If so, then the reverb driver tube and reverb transformer are working properly.

I have a Fender Vibroking that uses a 6V6 tube to power the reverb section. I already did the continuity test with my DMM on both RCA Leads and there is continuity meaning no broken or bent cables. I tested both ends of the reverb tank input measured 1.2k and output 200k. Guess im fine. How do you carry out this speaker test. I am 95 percent sure its the reverb transformer part number B-0047605000

https://www.tubeampdoctor.com/en/reverb-transformer-fender-vibroking-63-tube-reverb


I just want to be 100% sure the transformer is damaged before moving along with the purchase at TAD

[mresistor]

Jaquijano you need to start your own new post and thread,.. this thread is from 2017!! 

[tubeswell]

Ok pins 3 and 8 are 8v but pin 2 n 7 read -280 that pins 1n7 read -.871

You keep mixing up the pins. 

Pins 1 and 6 should be connected together.
Pins 2 and 7 should be connected together.
Pins 3 and 8 should be connected together.

You say "pin 2 n 7 read -280". I think you are misreading your meter. That can't possibly be -280 volts. Surely it's really -280 millivolts (which is really close to zero volts).

You also say "that pins 1n7 read -.871". Surely pin 1 and pin 7 are not connected together! Pin 1 and pin 6 should read several hundred volts. You recently said it was 360V.

Please look closely at your meter when measuring volts. Not just the numbers. If the display shows mV please tell us because it's important. And try to be accurate when you actually post the voltages. Don't mix up the pin numbers.

So, check those voltages again.

Also, here's a little test you can do... Connect a speaker to the reverb send jack. You should be able to hear your guitar through that speaker if you turn the dwell pot up. If so, then the reverb driver tube and reverb transformer are working properly.

I have a Fender Vibroking that uses a 6V6 tube to power the reverb section. I already did the continuity test with my DMM on both RCA Leads and there is continuity meaning no broken or bent cables. I tested both ends of the reverb tank input measured 1.2k and output 200k. Guess im fine. How do you carry out this speaker test. I am 95 percent sure its the reverb transformer part number B-0047605000

https://www.tubeampdoctor.com/en/reverb-transformer-fender-vibroking-63-tube-reverb


I just want to be 100% sure the transformer is damaged before moving along with the purchase at TAD

Do what sluckey said. Disconnect the reverb pan send cable and plug an 8 Ohm speaker to that instead. (You’ll need an RCA plug for the speaker lead). A fender reverb transformer is usually always a single-ended output transformer, so you’re effectively checking if the reverb driver circuit will function like a tweed champ. If it works like a champ, then you’ll know the problem is the pan input cable or input transducer coil.

[jaquijano]

Such transformer is damaged. I tried that test and could not hear anything in the external speaker even after setting the the dwell and mix controls of the reverb to full. I even connected the reverb tank of my red knob twin and no effect at all. What could have damaged the reverb tranny?

[tubeswell]

Such transformer is damaged. ...What could have damaged the reverb tranny?

Flyback voltage spike from the 12AT7 puncturing the transformer's winding insulation and shorting the transformer.


See this article for suggestions about preventative measures https://valvewizard.co.uk/reverbdriver.html