Issue With Bassman 5F6A Build

[martin manning]

I think the input jacks are good Tom. The resistance measurements look right now, unlike a couple of pages back when there were TRS jacks in there.

[Structo]

Thanks Martin.

I probably shouldn't post when I am under the influence of Percocet.

I have a nasty tooth ache.

[Guitarnut]

Did you try to check the idle current on the output tubes? The power tube pin 6 vs. pin 4 still looks odd.

Pin 8 to ground?

[ToneMerc]

Did you try to check the idle current on the output tubes? The power tube pin 6 vs. pin 4 still looks odd.

Pin 8 to ground?

Assuming you have the 1R resistor from pins 1/8> ground at each tube?

TM

[Guitarnut]

Did you try to check the idle current on the output tubes? The power tube pin 6 vs. pin 4 still looks odd.

Pin 8 to ground?

Assuming you have the 1R resistor from pins 1/8> ground at each tube?

TM

Not yet. I was going to add them with the bias test points. I drew this up for clarification. Does it look correct with and without the test points?

[Guitarnut]

I'm gonna go have a few beers and see if I can stop thinking about amps for the night.

As always, thanks to all for the continued help and support.

Hope you feel better soon Structo.

Peace,
Mark

[martin manning]

That's the right idea on the test points- ground the cathodes through the 1 ohm resistors, connect the black test jack to that ground, and connect the red test jacks to the cathodes.

On the V2 voltages:

V2
1 294vdc
2
3 2.06vdc
6 293vdc
7 248vdc
8 249vdc

Pin 1 and pin 7 have to be identical so there is a wiring error or maybe you have just transposed the 9 and the 4 on the pin 1 reading. Figure that out and then get the idle current dialed in.

[ToneMerc]

Pin 8 to ground?

Assuming you have the 1R resistor from pins 1/8> ground at each tube?

TM

Not yet. I was going to add them with the bias test points. I drew this up for clarification. Does it look correct with and without the test points?

In order to maintain the highest integrity of the cathode ground, I would not include the test points inline with the 1R resistor. There's several different ways to do this, all you ready need is a connection from the red jack tip to pin 1 or 8 and the ground connection to the blk jack tip.

Considering that the sockets are mounted on a horizontal plane and the minimal chassis real esate, I didn't even install test points on my 5F6A build as I had originally intended to. I left the upmost hole in pin one of each tube socket open and mounted a spade lug on one of the transformer support bracket screws, which just happens to make a nice press fit with the VM probe tip.

TM

[Guitarnut]

That's the right idea on the test points- ground the cathodes through the 1 ohm resistors, connect the black test jack to that ground, and connect the red test jacks to the cathodes.

On the V2 voltages:

V2
1 294vdc
2
3 2.06vdc
6 293vdc
7 248vdc
8 249vdc

Pin 1 and pin 7 have to be identical so there is a wiring error or maybe you have just transposed the 9 and the 4 on the pin 1 reading. Figure that out and then get the idle current dialed in.

Thanks. I'll recheck the readings in the morning.

Peace,
Mark

[Guitarnut]

In order to maintain the highest integrity of the cathode ground, I would not include the test points inline with the 1R resistor. There's several different ways to do this, all you ready need is a connection from the red jack tip to pin 1 or 8 and the ground connection to the blk jack tip.

Considering that the sockets are mounted on a horizontal plane and the minimal chassis real esate, I didn't even install test points on my 5F6A build as I had originally intended to. I left the upmost hole in pin one of each tube socket open and mounted a spade lug on one of the transformer support bracket screws, which just happens to make a nice press fit with the VM probe tip.

TM

So more like this.

[ToneMerc]

FYI, future reference you don't need to use a 5W 1R resistor, 1W is fine. I use the Dale CF1 1% series and the only reason I use a 2 or 3W is for visual symmetry, as the 1W in that series is awfully tiny and it just does not look right.

TM

[Guitarnut]

That's the right idea on the test points- ground the cathodes through the 1 ohm resistors, connect the black test jack to that ground, and connect the red test jacks to the cathodes.

Like so?

[Guitarnut]

FYI, future reference you don't need to use a 5W 1R resistor, 1W is fine. I use the Dale CF1 1% series and the only reason I use a 2 or 3W is for visual symmetry, as the 1W in that series is awfully tiny and it just does not look right.

TM

Yeah, I was thinking Mouser sent the wrong Rs. Ordered 5W but they look like 1/2 watt.

[martin manning]

Yes that will do it, but connect the test jacks to the terminal lugs, not the resistor leads. In your second drawing you shorted out the 1 ohm resistor.

[ToneMerc]

GN electrically it all works out the same, but here's an an example of the test point jack being separated from the cathode resistor path to ground.


TM