another issue with the twin

[Chickenwings]

the whole amp chassis seems to be microphonic. I have systematically checked and replaced every tube in the circuit so its not the tubes.
The amp works, but neither my 100watt marshall, nor my princeton combo do this - even when they are running with everything on 10.
when the amp is on if i tap in various parts of the chassis, the tapping gets amplified. if i turn the amp up, the tapping gets a nasty distortion to it.
The only way to stop the microphonic kind of sound and hum is to remove V2. But obviously, removing V2 means the amp no longer works at all.
I have tried various tubes in the v2 slot.
I also thought that perhaps the socket is loose, so i have opened it up, cleaned and checked all connections in there.
I have added cushioning inside the filtercap doghouse too.
All i can work out is that maybe part of the circuit somewhere is touching something it should not.
Im done. I cannot track down the problem any further than this.
Any ideas?

[drew_half_empty]

Re: another issue with the twin

the amp should work on the normal channel with v2 removed

try that and see if it still happens

[Chickenwings]

Re: another issue with the twin

well geez. i went out for a ride. came back and read your post, drew. so i double checked that v1 would work without v2 and it did....but somewhere along the way, the blasted thing decided to start working again properly! so i have screwed it all back together and i guess im done. .....
still no idea what caused it tho...

[Chickenwings]

Re: another issue with the twin

next thing to do is replace all the coupling caps inside (the filters have been done), then sand it back, fill the dings and scratches with wood filler and recover it in red with a wheat grille (maybe a new black faceplate too)

[MetalManiac]

Re: another issue with the twin

Microphonics? And your going to replace the caps? nah Brah. Youve got a bad tube socket. Wiggle the offending tube, and replace that socket.Youve got some arcing from some of the carbonized ( or something) tube pins.
I should add that this is a guess only based on very slight research.

[Chickenwings]

Re: another issue with the twin

Microphonics? And your going to replace the caps? nah Brah. Youve got a bad tube socket. Wiggle the offending tube, and replace that socket.Youve got some arcing from some of the carbonized tube pins.

i did wiggle all the connections and cleaned it out about an hour and a half ago. seems to be working okay now. when i replace the coupling caps i might re-do all the valve sockets as well...the thing is 44 years old so its probably due.

[crusty philtrum]

Re: another issue with the twin

Chopstick every component with the amp on and speakers attached. Also chopstick the valve sockets from inside the chasis. Chopstick the wires. Chopstick everything, including solder joins.

[Chickenwings]

Re: another issue with the twin

i feel like ordering some chinse food for some reason....


...yep no worries crusty, ill break out the chopsticks next time i pull it apart to do the caps and valve sockets. But seeing as its decided to work, ill just leave it as it is till then. Cheers!

[crusty philtrum]

Re: another issue with the twin

Do the chopsticking before you change any parts. (you can use a pointy stick instead of a chopstick, but make sure the safety-catch is on).

It's not worth doing amp upgrades on amps that have a problem, the problem needs to be fixed first.

[Chickenwings]

Re: another issue with the twin

yep will do. i will thoroughly chopstick it all before before i swap out any parts.. thanks man.

[drew_half_empty]

Re: another issue with the twin

Yeah old amps just have problems sometimes, I wouldn't ever plan to have one running 100% at any time. Mine's been doing this thing where if i try to just flip the switches and go it makes a crackly almost blown speaker-ish noise sometimes, but after it warms up for awhile it's fine. You just gotta learn the quirks.

It's like an old car. Even if you've replaced the engine & entire drivetrain, you're still dealing with 40 year old winshield wipers, starting mechanisms, door handles, window sealings, gauges... you get the idea.

Why do we love em? Cause they're awesome

[MetalManiac]

Re: another issue with the twin

.

Why do we love em? Cause they're awesome

Or get a Blackface point to point ..? ( I added the '?.'.see Ive made progress).
I don't think the Silverfaces- even the early point to point maybe.. hold up near as well as the old Pt. to Point blackfaces
Not lying ;I know a guy wiht a major collection of old Blackfaces, and even though one did smoke right in front of me, he refuses to do anything to restore any of them except play the rest in their original ( but admittedly pristine ) condtion As is!
As much as I protest, he runs them with the two prong cord, death cap , and all original caps and resistors...all of them, and his collection is sizable , and they all play just fine.
Amazing and STUPEFYING.
The guy leads a charmed life for sure.

[Bludave]

Re: another issue with the twin

God Bless man. I would have taken it to my tech right away.

[Chickenwings]

Re: another issue with the twin

Or get a Blackface point to point ..? ( I added the '?.'.see Ive made progress).
I don't think the Silverfaces- even the early point to point maybe.. hold up near as well as the old Pt. to Point blackfaces
Not lying ;I know a guy wiht a major collection of old Blackfaces, and even though one did smoke right in front of me, he refuses to do anything to restore any of them except play the rest in their original ( but admittedly pristine ) condtion As is!
As much as I protest, he runs them with the two prong cord, death cap , and all original caps and resistors...all of them, and his collection is sizable , and they all play just fine.
Amazing and STUPEFYING.
The guy leads a charmed life for sure.

this one is a 67. its the first run of silver plates, but still has the identical everything inside to the famous blackface amps of 3 months earlier. Ab763 circuit, ptp wiring, same caps, everything (except the face plate).
However it has had a filter recap, and new speakers (weber calis) and obviously the tolex was so battered a previous owner ripped it all off and just stained and lacqered the bare wood.