Gibson 1966 GA 55 RVT

[Big chief]

Purchased chassis of Gibson GA 55RVT sounds fairly well need some TLC
Need to know Resistor SK 250 10% that is all it shows What ohm is it as the end is broken off and can not get a reading  Please help

[sluckey]

Pictures. Schematic.

[DummyLoad]

schematic to reference would be nice... or a least a link to one.

--pete

[PRR]

Here's a plan with that number on it, but I don't see any SK, 250, or 10%. Gibson was known to change plans on a whim and never tell anybody.

[Big chief]

Please see photo

[sluckey]

I believe that says 3K. Not SK.

[Big chief]

So replace with 3k resistor

Many thanks

[sluckey]

You have two identical parts. I wonder what the other one measures.   

[Big chief]

37.42 ohm with fluke volt meter

[DummyLoad]

a little larger copy and perhaps a bit more legible.


-pete


EDIT: perhaps not!

[DummyLoad]

i believe that the two white parts are marked: 

SK
250
10%

are those the parts you're asking about?

--pete

[Big chief]

Yes trying to find what they are and what size they are so I can replace them any help would be great

[sluckey]

Disconnect the good one and measure it out of circuit.

[bmccowan]

might those be 250 pf capacitors? - I have removed similar looking & sized caps marked HI-K 250mmf 20%

[DummyLoad]

might those be 250 pf capacitors? - I have removed similar looking & sized caps marked HI-K 250mmf 20%

that's what i was thinking.


--pete

[Willabe]

might those be 250 pf capacitors? - I have removed similar looking & sized caps marked HI-K 250mmf 20%

Looks more like a cap to me. 

Measure it for capacitance.

Figure out what they are connected to in the circuit and that should tell you if their resistors or caps.

[Big chief]

As soon as I get home I’ll remove the good one and measure.
I have spent hours tracing the wires from Vi V2 V3 looking at the
Schematic can not locate any info on these components
Maybe I just don’t understand  Thanks for all your help

[sluckey]

I don't see anything on the schematic with a value of 250, but that's not unusual for a Gibson amp. That trim pot should be in the tremolo driver circuit. I would guess that the white component close to the trim pot is also in the tremolo circuit. If you can determine that either of those connects to a tube pin that would be a big clue.

[bmccowan]

C4 and C23 are both 250p on the schematic. C26 looks like 210p?
Agree that knowing what they are connected to will help a lot. It's very hard to tell on the photo.

[sluckey]

C4 and C23 are both 250p on the schematic. C26 looks like 210p?

Don't know how I missed those. C26 may be a 270p. That's a more common value. C4 and C23 should be easy to trace/identify since one end of each goes directly to a treble pot and nothing else.

[Big chief]

Disconnected component at top of photo meter set 20nf reading0.22 200nf 0.12
2000pf meter not stable

Disconnected component bottom of photo meter set 20nf reading 80 200nf 00.4

Wire from v3 pin 6 goes to right side of component v2 pin 5 goes to left of component

Is trem pot bias for 6l6. What ever I need will order from this web site

[sluckey]

Wire from v3 pin 6 goes to right side of component v2 pin 5 goes to left of component

Are you sure? That makes no sense.

Is trem pot bias for 6l6.

The trim pot is for the tremolo circuit. Look at the schematic.

[Big chief]

see photo

[Big chief]

I'm sorry did not know that trem pot was for tremola had never seen one
Please view photo of wiring from tubes

[shooter]

Finally got around to the schematics
Gibson has out-done itself   

[bmccowan]

Chief,
As Sluckey suggests, please check those connection points again. What you state would not be right, and it does not look that way in the photo to me, but the photo is still hard to see. For example pin 6 on V3 appears to be a blue wire that goes heads outside the chassis, which is consistent with the schematic.
Also - I think you probably need to suspect that previous work has been done and that it may have been done with mistakes/mods - some of the work looks a little suspect, even for Gibson.

[sluckey]

You need to practice counting tube pins.

[Big chief]

As the last photo shows I have put orange dot on wires
V3 pin 7 green wire to right side of component looking from back of amp
V2 pin 5 dark blue  wire to left side of component
Eyes must have been crossed
Do you think still 250 pf capacitor

Thanks for all your help I’m still learning

[bmccowan]

Do you think still 250 pf capacitor?

Yes, that's what I think they are. Others may differ.
Some additional things to consider. Given Gibson's tendency to constantly change circuits I snooped around on the web early this morning. I read that Gibson used the GA-45RVT circuit in some GA-55RVT models. I found that schematic which is much clearer than the GA-55 schematic - its attached. It includes those two capacitors (C41 & C43) but this time with a value of 500pf. This would also be typical of Gibson to change spec on small capacitors.
I'm also including a link to an article from a student who repaired and modded a 45 for a class project (i clearly wasted my time studying public policy!) It includes photos of the amp showing teal colored small caps in that location, and a schematic with some mods he did. Not vouching for what was done, but a lot of folks remove some of the extra circuit complications that Gibson added to 1960s amps.
https://courses.physics.illinois.edu/phys406/sp2017/Student_Projects/Fall02/MHerrmann/Mark_Herrmann_P398EMI_Final_Report.pdf
BTW, you are not likely to find 250pf caps that look like those today. Ceramic disc or silver mica are the probable choices.

[Big chief]

Thanks so much for the new information it was a big help
Many thanks to all the professional people that have helped me solve this problem

[Big chief]

Need help to hook up reverb tank as the amp has only 1 RCA socket for reverb tank
schematic shows 2 wires from tank I do not understand where to hook up second wire

Please help

[sluckey]

The tank input cable probably connects directly to the reverb transformer on the outside of the chassis. Probably solder connection.

[shooter]

look at the schematic, reverb section, top wire is a shielded cable (guessing rca jack)
the bottom wire shows a << for an unshielded wire, follow that line back to the parts n see if there's a stray wire or a broken off stub of wire

[sluckey]

The tank input cable probably connects directly to the reverb transformer on the outside of the chassis. Probably solder connection.

Yep. Except they used crimp stake-on connectors. See pic...

[Big chief]

Again many thanks made wire from transformer to input reverb
Works fine

THANKS