Robinette 6V6 JCM 800 build problem

[bobtait]

Can cap checks out with no shorts a little over 40 ohm 20 ohm 20 ohm 20 ohm

No input load on these voltages

B1 316V / B2 308V / B3 277V / B4 246V

Rectifier output 312V
Bias feed 54V

Pre Tubes:
Pin 1 2 3 6 7
V1 176V 140V 256V 196V 2.5V
V2 134V 38mV 26mV 135V 135V
V3 255V 95V 4.5V 253V 4.7V

Power Tubes: 5881
Pin 1 2 3 4 5 6 7 8
V4 2.5mV 5.5V 225V 259V -50mV 281V 5.5V 2.5mV
V5 1.5mV 5.5V 234V 260V -50mV 281V 5.5V 1.5mV

Amp still no output and getting too hot

[bobtait]

when I posted that the spacing creating Tabs disappeared but you can still tell which is which by the pin sequence

[JMPGuitars]

Post updated photos of the build, especially detailed shots of the power section.

[bobtait]

Here are some photos

[JMPGuitars]

Can cap checks out with no shorts a little over 40 ohm 20 ohm 20 ohm 20 ohm

No input load on these voltages

B1 316V / B2 308V / B3 277V / B4 246V

Rectifier output 312V
Bias feed 54V

Pre Tubes:
Pin 1 2 3 6 7
V1 176V 140V 256V 196V 2.5V
V2 134V 38mV 26mV 135V 135V
V3 255V 95V 4.5V 253V 4.7V

Power Tubes: 5881
Pin 1 2 3 4 5 6 7 8
V4 2.5mV 5.5V 225V 259V -50mV 281V 5.5V 2.5mV
V5 1.5mV 5.5V 234V 260V -50mV 281V 5.5V 1.5mV

Amp still no output and getting too hot

What are your PT specs? Do you know the brand/model or have the datasheet?

Your schematic has voltages for the B+ line and the power tube plates, and you're not close.

I don't think your PT can handle what you're trying to build.

Thanks,
Josh

[bobtait]

If you go back to page 1 of this feed you will find the data sheet for the Heybour transformer I used. It is actually very close to the one Robinette specs called for. But you know what, the truth is: (1) I should have never bought the amp that I gutted and tried to turn into this build. (2) I should have never bought the eyelet board that matched the Robinette design. I should have found or made my own tag board. (3) I should have planned out the exact placement of every component to ensure the shortest path to where everything has to go and I should have punched the chassis to accommodate that. I would have had a clean, neat hookup. But, this is a learning experience. Now, back to the mess I have created. I still firmly believe I blew or damaged the OT the first time I turned it on. I had everything hooded up ... except the damn ground wire to the negative side of the speaker jacks. I mean that is a disaster waiting to happen. Everything I have researched says that it is possible that that in and of itself could toast an OT. I mean I don't find buying another OT and patching it in to the circuit just to see what would happen. I can afford it and like I said this is a learning experience. I am just looking review of my mess. I also researched that a bad OT can skew every voltage measurement. If I have write this whole thing off and do something else, its not the end of the world. But, I would like to make it work. I have some kind of voltage every it is supposed to be, I think. I have had amps on my bench that had worse cable length runs or at least as bad as this one and they worked great. So, I dunno, what do you guys think? On a side note my fender PA 100 project is coming along great LOL.

[JMPGuitars]

It's definitely a learning experience. I think one of the best suggestions I can give you is to invest in good PTFE wire. It's much more forgiving to accidental iron contact...which you should still avoid.

I didn't see that part about you possibly frying it. You can get one and install it carefully, and see what happens. But did you do the other tests I suggested for the PT?

What B+ voltages do you get without the power tubes installed?

What B+ voltages do you get with the OT disconnected from cap can (still no power tubes installed)?

[Bieworm]

Apart from all the other things you need to fix, I am pretty confident I found your no-output-problem.
You seem te have shorted the hot lead to the speaker jacks to the negative (ground). This means that even though it's a switched jack the signal is always shunted to ground.
This is no input jack, so they don't need to be closed.
Clip that lead and be prepared for noise house of horror

[JMPGuitars]

You seem te have shorted the hot lead to the speaker jacks to the negative (ground). This means that even though it's a switched jack the signal is always shunted to ground.
This is no input jack, so they don't need to be closed.
Clip that lead and be prepared for noise house of horror

Nice catch! And the way it's wired can't be switched anyway.

[bobtait]

I clipped the leads off those jacks but still no sound. Does that mean I damaged the OT?

[bobtait]

still voltage on the OT primary and zero on the secondary.

[bobtait]

I guess if I wanted to emulate how a tweed deluxe only grounds when nothing is plugged in I would have just had the switched side connected to ground only on that side and wouldn't have left the wires running through both jacks.

[bobtait]

I am going to have to go through all the measurements again. When I clipped that mistake out the voltages shot up and stabilized. And if I do have the replace the OT the question comes up which one to try. The spec was for a Allen amps 7K:8-16 ohm, which is not available. The one I used was a Mojotone British 18watt 8K:4-8-16 ohm.

[bobtait]

Saw an earlier post I haven't replied to yet. All the wire in this amp except for the leads from the transformers and choke is 22 gauge PTFE wire mostly stranded except for the heater circuit which is solid.

[Bieworm]

Chances are high that the OT was fried due to the short. If you put a signal through the amp at higher volume for a while this could easily damage the OT. It’s also the possible source of the power transformer running hot.
When you disconnect the secondary wires and measure resistance between the hot and negative leads, what do you read?

[bobtait]

Here is a new development: When I touch pin 1 or 6 on the rectifier tube or pin 5 on the power tubes with the soldering iron tip I can hear buzz from the speaker connected to the output. So something is coming from the OT.

[bobtait]

Also it is not overheating anymore

[bobtait]

the resistance between all the secondary impedance wires is all .5 or .6 ohms either between each other or each one and the ground wire from the secondary

[bobtait]

I am getting 450v at the plates and most of the other measurements have doubled. I will take them all again and re submit.

[bobtait]

I checked my impedance selector switch and all 3 impedance wires were going thru the switch at the same time with continuity. I disconnected them and the switch was working as it should. But it seems there is a short on the output wires.