Whats on your amp workbench?

Amp tinkerers and people who aren't afraid of 700 volts or so in here....

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Re: Whats on your amp workbench?

Post by Bg »

https://www.temu.com/goods.html?_bg_fs= ... e_sn=10045

Not the greatest sound quality but good enough for my wife and her tin ears...
So, is that low alcohol or no alcohol at all? mmmm, no alcohol, do you want to try it? Noooooooooo.

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Re: Whats on your amp workbench?

Post by TmcB »

TmcB wrote: Sat Jun 15, 2024 8:35 am Ugh, customers Deluxe Reverb looks like it needs a new OT.

Came in with one dead power tube and a bunch of microphonic tubes.

Got new tubes that sorted out microphonics but I heard some weird crackle at higher volumes on certain notes.

Traced the noise to the power tube socket (can tap the tube to replicate) then to a blue wire. Thought it was a CEO solder joint but tapping the wire replicated the noise…followed the wire to the OT and on the outside of the chassis, if you tap the wire it makes the noise.

I think there’s a break in the wire somewhere from the OT to the socket that’s causing it to disconnect on vibration, which explains the dead power tube and the best solution is to replace the OT altogether.
Preeeetty sure it’s the tube socket now after swapping OT wires between sockets
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Re: Whats on your amp workbench?

Post by TmcB »

…it was the socket!
Note for others that Belton sockets are about 2mm wider that the ceramic ones so I had to find a step drill bit that was 30mm and wasn’t $200. Mike very graciously had a of raid his parts bin for a ceramic but didn’t end up being required.

Guy said it had never seemed right from new. Never heard how good it could/should be. He was absolutely chuffed.
GrantB wrote:Tony, your taste is, as always, very refined. Or as HG would say, "bloody awful".
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Re: Whats on your amp workbench?

Post by MikeC »

I've commenced a Princeton Reverb (AA1164) build for a change after building 8 x SRTs in a row! I've made the turret boards & installed the tube sockets. This one will be up for grabs if anyone is interested.
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Re: Whats on your amp workbench?

Post by hamo »

Bg wrote: Fri Jun 14, 2024 8:06 pm As some farcebook friends have seen, the missus wanted a Bluetooth speaker but hated the look. So I said I can build one into an old radio for her.

One visit to Temu later and it’s working surprisingly well.

2x3watts one speaker is the original rola.

Took bits out but left the tuning bits and the transformer for some reassuring weight.

Bluetooth and rechargeable battery.

Wife points well earned. 50s wireless that was buggered gets a new lease of life and a discreet rear control panel. Drilling Bakelite is not much fun but it worked out well - chain drilling then dremel.


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Re: Whats on your amp workbench?

Post by Bg »

hamo wrote: Wed Jun 26, 2024 2:25 pm
Bg wrote: Fri Jun 14, 2024 8:06 pm As some farcebook friends have seen, the missus wanted a Bluetooth speaker but hated the look. So I said I can build one into an old radio for her.

One visit to Temu later and it’s working surprisingly well.

2x3watts one speaker is the original rola.

Took bits out but left the tuning bits and the transformer for some reassuring weight.

Bluetooth and rechargeable battery.

Wife points well earned. 50s wireless that was buggered gets a new lease of life and a discreet rear control panel. Drilling Bakelite is not much fun but it worked out well - chain drilling then dremel.


IMG_1417.jpeg
Could be a nifty side hustle, throw a few together and set up a stall at the markets.
Have another couple on their way ;)
So, is that low alcohol or no alcohol at all? mmmm, no alcohol, do you want to try it? Noooooooooo.

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Re: Whats on your amp workbench?

Post by Jay »

What you say amp guys, is this red plating?

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Re: Whats on your amp workbench?

Post by jeremyb »

I think the northern lights have been captured in your toobz!
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Re: Whats on your amp workbench?

Post by Jay »

jeremyb wrote: Wed Jul 03, 2024 2:44 pm I think the northern lights have been captured in your toobz!
I don't think I have seen such a bad example. I wonder how the bias can drift so much to cause this. Any suggestions welcome
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Re: Whats on your amp workbench?

Post by jeremyb »

Jay wrote: Wed Jul 03, 2024 2:54 pm
jeremyb wrote: Wed Jul 03, 2024 2:44 pm I think the northern lights have been captured in your toobz!
I don't think I have seen such a bad example. I wonder how the bias can drift so much to cause this. Any suggestions welcome
Bias resistor failure? Or maybe power tranny failure causing too many volts to come out?
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Re: Whats on your amp workbench?

Post by RectifiedAmps »

Jay wrote: Wed Jul 03, 2024 2:54 pm
jeremyb wrote: Wed Jul 03, 2024 2:44 pm I think the northern lights have been captured in your toobz!
I don't think I have seen such a bad example. I wonder how the bias can drift so much to cause this. Any suggestions welcome
I don’t think drift can do that. It’d have to be a serious failure somewhere that’s messing up the bias.

Is it cathode biased? If so, the cathode bypass cap may be shorted. If it’s grid biased, something is messing with the negative bias supply- maybe a bad cap. Or else one of the 6V6s has a short from anode (or screen) to cathode or grid, which could then mess up biasing on both tubes.

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Re: Whats on your amp workbench?

Post by Jay »

RectifiedAmps wrote: Wed Jul 03, 2024 6:05 pm
Jay wrote: Wed Jul 03, 2024 2:54 pm
jeremyb wrote: Wed Jul 03, 2024 2:44 pm I think the northern lights have been captured in your toobz!
I don't think I have seen such a bad example. I wonder how the bias can drift so much to cause this. Any suggestions welcome
I don’t think drift can do that. It’d have to be a serious failure somewhere that’s messing up the bias.

Is it cathode biased? If so, the cathode bypass cap may be shorted. If it’s grid biased, something is messing with the negative bias supply- maybe a bad cap. Or else one of the 6V6s has a short from anode (or screen) to cathode or grid, which could then mess up biasing on both tubes.
I don't know how it is biased (yet). Last serviced by Clarry in 2014 and I don't think my BiL has looked after it kindly since.
Going to have a close look at it when I feel the urge :D
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Re: Whats on your amp workbench?

Post by Jay »

Had some weird crackling noise in the 4 twelve that took some time to fix. Easiest was swapping all four valves out but that didn't solve it. Playing with the controls, i decided it had to be in the second triode in the 1st preamp valve. Swapped anode and cathode resistors. No luck. Then thought it had to be in the triode folowing the tonestack. Changed the same components. No luck. So on to the phase invertor triode. Quite tricky to change those components so decided to reflow the valve pins solder first. Fixed.

What a hunt :(
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Re: Whats on your amp workbench?

Post by MikeC »

Checking out murky's 1974 USA Silverface Super Reverb - it's the AA270 circuit (with 5U4GB rectifier). Not sure when last used but I've had (115V) mains on her (with no tubes) and the PT is intact. I'll replace all of the old leaking Mallory dog house filter caps & test all the tubes before I power her up with the rectifier and check her out more thoroughly. I am being very careful with this one & won't replace anything other than the absolute necessaries. She looks to be in pretty good order apart from alot of wax on the board/components which can become conductive. We'll see...

I just dated the Schumacher PT to the 51st week of 1973.
Th Fender serial no (stamped into chassis) dates it at 1974.
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Re: Whats on your amp workbench?

Post by Cdog »

A well preserved specimen...That will be fun

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