Whats on your amp workbench?

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

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Cdog
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Re: Whats on your amp workbench?

Post by Cdog »

Awesome! 8)

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Re: Whats on your amp workbench?

Post by Lostininverness »

PaulWD wrote:Just tried this out tonight. It's a 5e3 with robrobinette's mods, master vol, lead and normal channel. Its consideribly easier to overdrive compared to stock 5e3's. It's quite crunchy.

I need to get some more dial bulbs. I am using the old radio dial lights as an indicator.

The radio/pa would have originally done duty in a school or motel
IMG_20200214_192810.jpg
IMG_20200214_192923.jpg
I'm impressed with your ability to place all the components where you need them without using a board! And its still quiet? Very cool!

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Re: Whats on your amp workbench?

Post by Reg18 »

PaulWD wrote:Just tried this out tonight. It's a 5e3 with robrobinette's mods, master vol, lead and normal channel. Its consideribly easier to overdrive compared to stock 5e3's. It's quite crunchy.

I need to get some more dial bulbs. I am using the old radio dial lights as an indicator.

The radio/pa would have originally done duty in a school or motel
IMG_20200214_192810.jpg
IMG_20200214_192923.jpg
I had the Robrobinettes MV and NFB mods done to my old 5E3 and always wanted to try the lead channel one too, be keen to here this one some time.

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Re: Whats on your amp workbench?

Post by PaulWD »

I'm impressed with your ability to place all the components where you need them without using a board! And its still quiet? Very cool!
Yes, it's not too noisy. I got into the amp hobby after restoring vintage radios. Not a board in site with those.

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Re: Whats on your amp workbench?

Post by PaulWD »

Reg18 wrote: I had the Robrobinettes MV and NFB mods done to my old 5E3 and always wanted to try the lead channel one too, be keen to here this one some time.
I'll bring this and a few others to the next CHCH gearfest.

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Re: Whats on your amp workbench?

Post by PaulWD »

Mike Clayton wrote:That's kind-of point to point wired with a couple of tag boards. Cool!
Cheers. My mentor was an old telecom engineer. He doesn't use group boards at all. One day I hope to get my layouts as refined as his. I am sure I could cut down the wire length. I would like to also try lacing at some point to get things neat.

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Re: Whats on your amp workbench?

Post by Lostininverness »

PaulWD wrote:
I'm impressed with your ability to place all the components where you need them without using a board! And its still quiet? Very cool!
Yes, it's not too noisy. I got into the amp hobby after restoring vintage radios. Not a board in site with those.
I've got a few old ones in non-working condition that I was going to play with, but not enough time means they are just gathering dust. Do you want them?

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Re: Whats on your amp workbench?

Post by MikeC »

My '64 Vibroverb chassis wiring is now complete. Kind-of aimed for the vintage Fender wiring style this time which looks a bit messier but at the same time more "correct"(?) Anyhow, will be dragging out the VARIAC and light-bulb current limiter for first time power up very soon...
Finished Chassis Topside#1.jpg
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Re: Whats on your amp workbench?

Post by Cdog »

Looking great Mike! :)

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Re: Whats on your amp workbench?

Post by MikeC »

Cdog wrote:Looking great Mike! :)
I've just finished the power up tests and have her running. I had a few issues - 1. Overlooked the wiring of the power tube negative BIAS supply (doh!) and 2. Had the bias supply diode reversed (thus providing positive bias!!), but I picked up and fixed both issues before the 6L6's were installed. 3. Had a "squeal" which turned out to be caused by the negative feedback acting as positive feedback - I swapped the OT wires over on pin 3 (plates) of the 2 x 6L6's - and that's fixed! 4. When vibrato is on I have audible tremolo tick/thump through the speaker which is at a constant level regardless of the volume pot settings - it's apparently quite common on AB763's. Lead dress adjustment didn't make any difference so I tried wrapping the tremolo control leads with a grounded wire, which has reduced it. But it's still audible (and annoys me) so I googled it - the solution apparently is to add a grounded .01uF cap across the roach. Will post the results when I've added the cap!

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Re: Whats on your amp workbench?

Post by robthemac »

Mike Clayton wrote:When vibrato is on I have audible tremolo tick/thump through the speaker which is at a constant level regardless of the volume pot settings - it's apparently quite common on AB763's. Lead dress adjustment didn't make any difference so I tried wrapping the tremolo control leads with a grounded wire, which has reduced it. But it's still audible (and annoys me) so I googled it - the solution apparently is to add a grounded .01uF cap across the roach. Will post the results when I've added the cap!
Let me know how that goes! My Vibrasonic has the same tick.

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Re: Whats on your amp workbench?

Post by RectifiedAmps »

Mike Clayton wrote:
Cdog wrote:Looking great Mike! :)
When vibrato is on I have audible tremolo tick/thump through the speaker which is at a constant level regardless of the volume pot settings - it's apparently quite common on AB763's. Lead dress adjustment didn't make any difference so I tried wrapping the tremolo control leads with a grounded wire, which has reduced it. But it's still audible (and annoys me) so I googled it - the solution apparently is to add a grounded .01uF cap across the roach. Will post the results when I've added the cap!
This was such a common issue for Fender back in the day that they issued a service bulletin on it:

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Re: Whats on your amp workbench?

Post by MikeC »

That's the one, thanks. I prefer bias wiggle trem like on Princeton, do you know why they went to the optocoupler?

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Re: Whats on your amp workbench?

Post by Cdog »

I put a cap across my roach too.... Used a 27n as that's what I had at the time. It smooths the waveform a little, but still sounds good.

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Re: Whats on your amp workbench?

Post by MikeC »

Cdog wrote:I put a cap across my roach too.... Used a 27n as that's what I had at the time. It smooths the waveform a little, but still sounds good.
Interesting, that's twice+ the value of the recommended cap (.01 uF). It must be effecting the neon's pulsing waveform - did you see the tremolo waveform change on an oscilloscope?

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