6AQ5 glow test failure - socket B only [solved]

Loquah · 5812

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Offline Loquah

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on: July 09, 2022, 12:34:39 AM
I'm stumped!

I've reached the second glow test and the D socket tube glows happily, but the B socket tube doesn't.

I've tried:
  • switching the tubes over - no change, the socket is the issue, not the tube
    • double checked all wiring connections to confirm they matched the instructions
    • reflowed solder joints on the B socket (B3 & B4)

    I can't work out how the D side is working when the B side isn't given that the D socket takes it's heater power from the B socket!?
« Last Edit: July 19, 2022, 01:41:03 PM by Loquah »

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Offline kgoss

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Reply #1 on: July 09, 2022, 03:36:37 AM
Post pictures and trace the voltage with your meter to find out where it stops.

Ken Goss


Offline Doc B.

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Reply #2 on: July 09, 2022, 05:20:58 AM
The most likely possibilities are that a tube pin is not making contact in either B3 or B4, or that there is a miswire on that socket.

Dan "Doc B." Schmalle
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Offline Loquah

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Reply #3 on: July 09, 2022, 01:05:27 PM
The most likely possibilities are that a tube pin is not making contact in either B3 or B4, or that there is a miswire on that socket.

Thanks Dan! I think that's the issue given that the D socket works perfectly. Any tips for realigning the contacts in the tube socket?

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Offline Loquah

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Reply #4 on: July 09, 2022, 01:09:18 PM
Just found some info about adjusting the sockets from the top with a jeweller's screwdriver. I'll try that, but welcome other tips

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Offline Loquah

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Reply #5 on: July 09, 2022, 04:02:37 PM
I just had a close look at the tube socket in question and pins 3 & 4 look fine, but pin 7 shows no sign of any contacts inside the socket!

Does this look strange to you?

https://photos.app.goo.gl/gZ64mziWxVbXpSMdA

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Offline Thermioniclife

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Reply #6 on: July 09, 2022, 06:36:16 PM
I do not believe pin 7 is used on a 6aq5.

Lee R.


Offline Loquah

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Reply #7 on: July 09, 2022, 06:37:56 PM
I do not believe pin 7 is used on a 6aq5.

That's possible, but I'm wondering if there's a deeper fault with the tube socket given that the contacts seem to be missing entirely and the tubes both work when transplanted to the D socket.

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Offline Doc B.

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Reply #8 on: July 10, 2022, 04:02:14 AM
Yes that definitely looks odd. Does the pin 7 terminal protrude farther on the underside than the others? If it doesn't look like something that can be adjusted we can certainly send you a new tube socket and whatever you might need to replace that is connected to it.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Loquah

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Reply #9 on: July 11, 2022, 04:22:16 PM
Yes that definitely looks odd. Does the pin 7 terminal protrude farther on the underside than the others? If it doesn't look like something that can be adjusted we can certainly send you a new tube socket and whatever you might need to replace that is connected to it.

On the bottom, the pins look fine, but they look misaligned. It's hard to describe, but when you look from the top at both 7-pin sockets, the orientation is identical (i.e. the angle of where the gap in the pins points is the same). When you look at the bottom of the chassis, the placement of the pins is slightly different between B & D sockets. I wonder if the moulding of the socket went wrong for the one in Socket B. I've ordered a set of new sockets from a local retailer for the sake of time and happened to go gold because that was the only option on the 7-pin sockets so I wanted them all to match.

I'll provide an update when I install the new sockets to confirm if the problem is resolved.

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Offline Doc B.

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Reply #10 on: July 12, 2022, 05:29:38 AM
Shoot, sorry about that. I'll have a look at our socket stock and see if that was a one time thing or not.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Loquah

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Reply #11 on: July 12, 2022, 03:31:43 PM
No problems at all. I've attached some pics of the tops and bottoms so you can see what I mean about them being perfectly aligned from the bottom, but different when you look at the top.

https://photos.app.goo.gl/FTweaXvvVgW2U4Ey6

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Offline Doc B.

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Reply #12 on: July 12, 2022, 03:55:29 PM
Son of a gun. It looks like the top rotated one full pin hole relative to the bottom before it was put together. Not only do you have a hole with no terminal, you have a terminal with no hole. First time I have seen that in 30 years of doing this stuff.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Paul Birkeland

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Reply #13 on: July 12, 2022, 04:48:11 PM
That is really strange to see, but I'm glad that the glow test caught this before you built the rest of the amp out!

Paul "PB" Birkeland

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Offline Loquah

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Reply #14 on: July 12, 2022, 08:08:38 PM
Son of a gun. It looks like the top rotated one full pin hole relative to the bottom before it was put together. Not only do you have a hole with no terminal, you have a terminal with no hole. First time I have seen that in 30 years of doing this stuff.

I guess I'm just special!  ;D

I agree, Paul. Having returned to building BH kits for the first time in a while, I'm a big fan of the regular checkpoint tests. Great addition!!

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