Old Gibson Stereo Amp Cap Question

[sr1200]

So I found a place in PA that does vintage speaker repair.  All the places by me got terrible reviews including one where they irreparably damaged the speaker they were sent.  Does anyone have someone reputable in the north east (US) that they recommend for this type of work.  The surrounds look like they're holding up pretty well (no visible tears or holes), but they are dry and flaky to the touch, so I really should have them taken care of professionally.

Did I get the fuzzy resistors and caps right? 

I was planning on going to justradios to get replacement caps for this since they have some higher voltage caps and they also have a 20uf + 20uf can that can replace the dyn-O-myte!  The spragues on the turret board, should I replace with film or electrolytic?

 

[andyfromdenver]

So I found a place in PA that does vintage speaker repair.  All the places by me got terrible reviews including one where they irreparably damaged the speaker they were sent.  Does anyone have someone reputable in the north east (US) that they recommend for this type of work.  The surrounds look like they're holding up pretty well (no visible tears or holes), but they are dry and flaky to the touch, so I really should have them taken care of professionally.

Did I get the fuzzy resistors and caps right? 

I was planning on going to justradios to get replacement caps for this since they have some higher voltage caps and they also have a 20uf + 20uf can that can replace the dyn-O-myte!  The spragues on the turret board, should I replace with film or electrolytic?

haha! still unsure where the fuzzy caterpillars and caps lead . would need to see it in person and trace it out. do they say 200ohm perchance?

so I attached a pic with all the elytics to replace.
you know the 4 in the power section (two in the pwr chassis and two in the stick o D)
need to be 450V.

the rest are 20-25uf 25V, except the two off power tubes, get 25-50uf/ 50V

just get elytics. can bulk order 10 x 25uf/ 50V and save some $.

The resistors look like Allen Bradley, I don't personally find that they drift as bad as some of the cheap pieces of crap from the era .

In my opinion only, I say just deep clean, recap, retube, replace the cord, and then see whats what.

I also arrow'd the cap I believe someone mentioned earlier off the ground/ polarity switch.

 

[sr1200]

Thanks

To me the fuzzy's look to be the ones you circled between v 4 and 5 and v7 and 8.  They have a ground wire and there are 2 leads that go out to the right board and to the tubes.

I contacted the guy in PA about the speakers, im going to make a road trip possibly tomorrow to get them over there (takes 14 business days to turn around and are $56 each (not terrible i feel) and the guy has nothing but rave reviews.  Felt like i was talking to David from cinemag when i was on the phone which gave me a good feeling.

 

[sr1200]

I would suggest avoiding NOS electrolytic can or tubular caps unless you're just going to play amp every now and then and don't care if they short out at random times.  They eventually will and will probably be noisier than new production.

its not NOS parts, its just parts that aren't easily attained elsewhere.  (they have funky values that I dont see at mouser, digikey etc.)

 

[sr1200]

Just a quick update and some new pics.

PowerSupply:
https://files.mycloud.com/home.php?brand=webfiles&seuuid=e703c2aa7c1b287c4b3fd9d59eb1300c&name=IMG_2620
Speakers:
https://files.mycloud.com/home.php?brand=webfiles&seuuid=45ceabf4c0b917eda8a6edd5b064722c&name=IMG_2621

So the speakers actually dont look as bad as they did through the grille cloth.  There was just a tonne of dirt and dust, but once cleaned, they're not that crusty.

The power supply on the other hand... the big cap (wasn't expecting another stick of dynamite) and the resistors look totally shot.  Once of the resistors is crumbling apart (should i shoot for 5 or 10 watt on those as a replacement?)  The cap, i ordered individual caps, (2 20uf 450v) hopefully that will work just fine instead of the boom stick.

 

[andyfromdenver]

Just a quick update and some new pics.

PowerSupply:
https://files.mycloud.com/home.php?brand=webfiles&seuuid=e703c2aa7c1b287c4b3fd9d59eb1300c&name=IMG_2620
Speakers:
https://files.mycloud.com/home.php?brand=webfiles&seuuid=45ceabf4c0b917eda8a6edd5b064722c&name=IMG_2621

So the speakers actually dont look as bad as they did through the grille cloth.  There was just a tonne of dirt and dust, but once cleaned, they're not that crusty.

The power supply on the other hand... the big cap (wasn't expecting another stick of dynamite) and the resistors look totally shot.  Once of the resistors is crumbling apart (should i shoot for 5 or 10 watt on those as a replacement?)  The cap, i ordered individual caps, (2 20uf 450v) hopefully that will work just fine instead of the boom stick.

haha!  I'm kind of hoping you got two radial caps for the power chassis. Seems like there is probably a way to work it on that tag strip.

yes the catapillars can be nothing other than the pwr tube cathode resistors. I finally see the polarity markings. Those should be min 5 watt if you didn't already know.


great that you are getting new/ repaired speakers.

I hope someone more knowledgable comments on the Secondary series resistors. The need/ benefit etc.
Sometimes stuff can be power sized on the edge of/ at rating limits as a sort of fuse.
I found that out with a recent amp with an old voltage regulator tube.

 

[sr1200]

Took the speakers over to the guru of speakers.  After testing them on some crazy contraption he said he wouldn't touch them as they are now and they're probably the best conditioned speakers for their age he's seen.  (normally, the speakers have little holes in the surrounds and cones... nothing on these) So, yay i saved $120 but I also drove about 400 miles to find that out so I'd call that a break even. 

Caps should be here by monday I think.  While the tube sockets are still in great shape the rubber grommets are very tired.  The sockets are riveted to the chassis.  Any easy way to remove those, or is it drill time for them?

 

[CJ]

drill time  :-\

 

[sr1200]

https://files.mycloud.com/home.php?brand=webfiles&seuuid=0fafdede08e7e9dd711069e3abc0b512&name=IMG_2631

Im guessing these are caps as well.  once the heat from the iron went near them they started sweating pretty bad.

Not quite sure how to read this, but red green brown white would be 250 (WHAT) with a 9% (?) tolerance?

 

[abbey road d enfer]

Not quite sure how to read this, but red green brown white would be 250 (WHAT) with a 9% (?) tolerance?

I would say it's one of the 250pF in the tone stack, probably a silver dot that indicates 10% tolerance IINM.

 

[sr1200]

i have 2 red green brown white (or possibly silver...) and 2 green black brown white (or silver)

If i had to guess they would be the two caps that are found in the schematic by the PHONO jacks that are listed as 250uuf (micro micro farad?) and 500uuf just after V2.

 

[sr1200]

Finally got all the parts, replaced all the caps and did the diodes in the PS (the old ones were leaking some kind of brown fluid... didn't know diodes were liquid...) Replaced a few of the tube sockets and replaced all of the rubber grommets.

A few of the tubes had bare wires running from the rivet holding the sockets in place to the chassis... dont know what this does, but i tried to emulate it by hooking that bare wire up to the screw that now holds the sockets in place.

I powered it up with the variac SLOWLY.  Brought it to 110 just to start (the unit and the schematic say its good to 125vdc)

VERY little sound, and the power tubes are getting UBER hot.  Tube 2 and 3 are not lighting up (filaments are powered properly getting 6.2vac at the heaters).

The schematic only lists 3 points of voltage besides the tubes. 
The power supply voltage ref is +335v im only getting 309, but that climbs up accordingly if i bring the mains power up to 120.
The second is just after the 10K resistor that is fed from the rail that leads to the screen grids off V4/5/7/8.  Reference is +275v, im getting 285 (not terrible, but is even worse if i bump to 120)
The third is after the second 10K resistor on that rail (listed to the right of the V1 on the schem)  Reference is +245v, Im getting 279.5

Tubes are A MESS

V1	Fil	Fil	0	1.44	0	209	3mv	0	1mv
V2	Fil	Fil	0	0	0	285	285	0	0
V3	Fil	Fil	0	0	0	0	281	0	0
V4	0	0	12.65	Fil	Fil	0	304.6	0	307
V5	0	0	12.65	Fil	Fil	0	304.6	0	307
V6	0	0	0	48.2	35.2	243.5	242.5	35.25	48.2
V7	0	0	12.36	Fil	Fil	0	305	0	307.7
V8	0	0	12.36	Fil	Fil	0	304	0	307.7

Need to figure out whats up with V2 and 3 first perhaps?

As always suggestions appreciated and welcome  ;D

 

[abbey road d enfer]

A few of the tubes had bare wires running from the rivet holding the sockets in place to the chassis... dont know what this does, but i tried to emulate it by hooking that bare wire up to the screw that now holds the sockets in place.

Grounding unused pins and shields was very common practice.

VERY little sound, and the power tubes are getting UBER hot.

Have you checked the voltages without the tubes (except the rectifier) before loading the power tubes?
Do they glow red? Power tubes do get hot. You mut check the current, by measuring the voltage across the cathode resistor. Should be around 13V.

  Tube 2 and 3 are not lighting up (filaments are powered properly getting 6.2vac at the heaters).

You need to check the DCR with an ohmmeter; very likely the heaters are open.

ref is +335v im only getting 309,

Don't be obsessed; 10% , even 20% variation is acceptable.

The third is after the second 10K resistor on that rail (listed to the right of the V1 on the schem)  Reference is +245v, Im getting 279.5

Since two tubes are evidently not working, they don't draw current, so there's no voltage drop.

 

[sr1200]

;D. So i put the old tube sockets back in the amp. Fired up. Sounds AWESOME!!  Its like dick dale meets james bond!

I sincerely thank everyone that helped out with info and suggestions. 

I plan on using it on a project soon, ill post some audio when thats done. Again, many thanks to a great community!!!