1962 Vibrolux squealing

[Chuck H]

If you mean you read 73mV across the 1 ohm resistor, that seems either very high or a little low. It depends on whether you had both cathodes running through it or just one.

Good troubleshooting on the solution. As Jazz mentioned, the colors aren't always accurate. I don't know why transformer manufacturers seem so prone to this but I've even seen secondary taps incorrectly coded. Good thing they always get the red lead correct

And good job getting the customer to replace the filters (since he likes original). That's a biggie for a lot of amp collectors because new ones look nothing like the originals. Especially the big old can types. My reasoning with the customer is usually along the lines of "Well, the amp wasn't built with bad filter caps so your old broken ones aren't like it's suppose to be either." I hope you got him into a grounded AC cord.

[sleepingAwake]

If you mean you read 73mV across the 1 ohm resistor, that seems either very high or a little low. It depends on whether you had both cathodes running through it or just one.

Good troubleshooting on the solution. As Jazz mentioned, the colors aren't always accurate. I don't know why transformer manufacturers seem so prone to this but I've even seen secondary taps incorrectly coded. Good thing they always get the red lead correct

And good job getting the customer to replace the filters (since he likes original). That's a biggie for a lot of amp collectors because new ones look nothing like the originals. Especially the big old can types. My reasoning with the customer is usually along the lines of "Well, the amp wasn't built with bad filter caps so your old broken ones aren't like it's suppose to be either." I hope you got him into a grounded AC cord.

Yeah that reading is on each separate cathode. Way to high.
I'm getting around 428v B+ and -31v at the power tubes.

The amp or may not have cut out on me tonight. I couldn't tell if it was the amp or guitar.
I know that sounds strange but it only did it a couple times.

I replaced a bad power switch, a cheap volume pot, all tubes, all electrolytics, re soldered every connection, swapped out the screen resistors for metal film, removed the death cap and added a three prong plug.
All that stuff is maintenance. If I replace the rest of the astrons and every carbon comp I might as well not call it a fender anymore.

[Chuck H]

Sure it's still a Fender!!! They didn't ship them with worn out parts!!! If it's a player it's gotta be maintained! JM2C on that. The three prong cord doesn't change a thing about the sound (Except that it may hum less) so that's just a contemporary safety code UPGRADE.

You should cool off the bias though. Adjust it to about 75% max plate dissipation at idle and listen to the trem at a fairly extreme setting. If it's garbling too much heat the bias a little and see if that helps.

[Mick Bailey]

I saw some replica Astron caps - the person or company that made them had tooling made up to mould the casing so they looked original.

I guess Mallorys could be overmoulded and printed up to give a good performing cap with the correct appearance. I do like to keep these vintage amps looking original as far as is practical. It's a shame when you get a virtually unused amp from the 50s or 60s that needs 50% of the components replacing with modern versions.

When you look at restoring old buildings though, the approach is to cut in a brand new piece of stone and make no attempt to blend it in or colour it to match the original. As an ex-colleague of mine used to say "nothing wrong with a good honest repair."

[sleepingAwake]

Well a little more progress and some setbacks.

I substituted the 43k ohm bias resistor for a 47k and that got the bias voltage down to -33.4 at the tubes.
The cathode resistors now show 50mv and 47mv respectively.
Which is much better than the 70mv+ I was hitting.

Now I'm on to another issue.
I have it sitting on my bench without anything plugged into it.
I'm monitoring bias voltage and it starts to cut out again.
It made a little thump thump and came back on after a few seconds but I wasn't quick enough to check other voltages.

I cleaned and re tensioned all tube sockets prior to the repair work.

[Chuck H]

Maybe run a shop radio through it during the burn in time so you can hear what happens to the signal when it cuts out. Not sure why it would do that just sitting at idle though.?. I've heard new tubes make funny noises for no provoked reason. Usually it's a white noise that starts out of the blue, rises in volume briefly and then ends with a "pop", thump, "pa-pop" or "thu-thump".

Have you tried smacking the amp to see if you can induce the failure with vibration?

[sleepingAwake]

Maybe run a shop radio through it during the burn in time so you can hear what happens to the signal when it cuts out. Not sure why it would do that just sitting at idle though.?. I've heard new tubes make funny noises for no provoked reason. Usually it's a white noise that starts out of the blue, rises in volume briefly and then ends with a "pop", thump, "pa-pop" or "thu-thump".

Have you tried smacking the amp to see if you can induce the failure with vibration?

I'll be damned Chuck you just described the noise exactly.

I've been trying to play through it (its such a chore but maybe I'll just take your advice and hook up a shop radio.
I'm also thinking of going up to a 100v bias cap since I'm running dang close to 50v. Say -47.5. I'd have to order one however and the owner will have to wait longer.
That might be or the best. I tested two of the coupling caps and one leaked 5v and the other 2v. Suffice to say they are all probably leaking.

I should add the amp sounds even better bias'd at 50mv. So sweet and smooth. If only I could keep it.

[Justin Thomas]

I would recommend checking the caps individually - it's not THAT many! My buddy's Hammond has several hundred... If you wanna hear yourself play through it while you work on it, that's what delay pedals with loop features are for!

My 67 Bassman used to make the same kinds of noises - it'd sound like bacon a few seconds, going up in volume, then popping a bit or a slight crackle, then quiet. Repeat every ten minutes. It was never horribly loud, but enough to be distracting. I started at the preamp plate load resistors; it turned out to be the channel mixing resistors - well, it 95% went away when I replaced them both... I left in as many original parts as I could, though...

For your concerns about it "still being a Fender" IF you do replace every part in it - my 62 Concert has all the original carbon comps, but 4 Celestion speakers. Some "indiscriminate" person replaced EVERY capacitor in it with cheapies. That the resistors are original but the caps replaced, I think someone took a "cap job" a little too far. But - It STILL sounds 100% Fender! I know the amp has seen water damage at some point...

Take the time to check it thoroughly without jumping to conclusions - the amp & owner will thank you, and you'll thank yourself later! Plus, it's practice! Good luck,

Justin

[Chuck H]

+++

The new tubes are certainly top of my list for the noises but CC resistors are known for it too. Justin gave a good description of the noise they make. So there's another go to possibility. If the tubes are making the noises it may, or may not stop once the tubes break in awhile. It seems that JJ power tubes are especially prone to it from my own experiences and what I've read here. As to CC resistors, it's usually the plate loads. But I'm learning now that the mixer resistors may get involved too.

As to replacing parts, try this. Be careful removing any parts from now on. Take the old parts, put them in a plastic baggie and give them to the customer. Explain that they were bad. Tell him you for an additional charge you can put them back in if he would rather have his amp in original, broken condition.

Honestly!?! If it's a museum piece you want it to be 100% original (working or not, it doesn't matter). If it's a collector you fix what's broken with OEM parts if you can get them. Closest to original if you can't. If it's a players amp you should use the best parts for the job because the amp needs to work. In any case, when it comes to vintage amps I always save the original parts in 'as pulled' condition and return them to the customer.

[sleepingAwake]

So after much troubleshooting and testing...

One of the RCA preamp tubes I was hopeful about was bad. Something internal made a popping noise when it was vibrated.
New Sovteks throughout per the customers request.

I ended up having to replace all of the yellow astrons. I tested each individually and they all leaked. Even those in the tremolo section were bad.
Replaced them with Mallory 150's.

Tubes are idling at 48ma
Plate voltage at 449v

Amp sounds great and is super quiet. No more cutting out after letting the amp burn in for a few hours. Tremolo is crazy deep.

Thanks everyone for your help.

[Tone Meister]

Good work! I sure enjoyed watching you folks suss this one out. This is one for the archives.

[sleepingAwake]

UPDATE!!!

The owner ended up wanting to sell it.
I made an offer of $600 and he accepted.

I have probably a little under $800 into the amp after the purchase price.

Gonna make a baffle for it and tuck the old one away somewhere. The original grill material is dry rotted and torn in spots but I'm sure someone would prefer the original if I ever end up selling it. Might as well keep it safe somewhere.

I'd like to clean up the tolex some and polish the rust off the chassis straps.

[Chuck H]

Even in rough cosmetic condition that amp is a score at that price. Nice.

[sleepingAwake]

Well it isn't exactly in rough shape

Do you think it hurts the value to swap out the handle and grill cloth? Let's say I threw the old grill cloth out.(haven't of course).