unknown amp and old caps

[davohilts]

I've obtained an old amp that I am hoping to identify so I can try and find a schematic. It also has some old caps I can't identify and need some help.
The first cap is a molded mica cap with two rows of colored dots. The top row has arrows and the colors are black, red, violet in the direction of the arrows, the second row is brown, gold, brown. Does this mean that it is a .02 mfd cap?
The second one is a brown cardboard covered cap with a marked positive end. It is labeled:
3 ohm Z 1-1/2V
12 45
K12U568 13
I will attach pics and thanks for any help.
The amp uses a 35Z5GT rectifier tube, 2 50L6GT Power tubes and 2 12AX7 preamp tubes. The amp has an input jack labeled Mike above and Accordion below, followed by 3 input jacks labeled above 'for studio' and below instruments, followed by Acc & Mike volume control, followed by instru. volume, followed by power switch/tone control labeled tweeter/bass, then power light and fuse.
It came in a nice wood cabinet with a 12" alnico speaker and small tweeter each fed from the OT using a 5mfd/50 volt cap.
Sound familiar??

[nashvillebill]

There's TWO 50L6's??

[Jazz P Bass]

Please be real careful digging around in the amp with it under power.
That tube set sounds like the amp runs directly off of the mains.
No isolation transformer.

[g1]

I'm sure I was able to see the attached pictures before, now they are gone.
Something still seems to be eating the attachments.

[davohilts]

I don't know what happened to the pics I posted. When I get back to my laptop I'll repost them.
Yes, there are two 50L6 tubes and there is an isolation transformer. What I'm gonna do is remove the circuit board and rebuild it exactly as it is. I'll take some pics of the chassis gut without the board which is installed vertically and supported by heavy ground wires going into the chassis rivets in two places, I plan to install some clip angles for better support.
My main issue right now is identifying the caps that I don't understand.
thanks for the help.
Dave

[DrGonz78]

You can say or type that again...

As of today around 1am or so there has been a problem with attachments and creating new ones. It seems maybe there is something going on within the site to fix or troubleshoot the attachment problem. However, we are not really kept up to date to know any of this and it really only keeps us guessing like idiots.

[davohilts]

well, the thumbnail pics are back but when you click on them you get nothing. baby steps maybe?

[nashvillebill]

It could be like several others, including a Lectrolab amp I owned, which have a transformer for B+ but the heater filaments are run directly off the 110 coming in. Not truly isolated, but not a hot chassis either. I suppose the two 50L6's could have their heater filaments in parallel, then the 35 and 12's are in series with the 50's.

Did you follow this site to identify the domino caps? Replacing Capacitors in Old Radios and TVs

[davohilts]

Lectrolab was a good lead but alas no dice. Your assessment of the circuit is pretty much right on. The power transformer is powered from the fuse which also has a wire running to pin 8 of the 35Z5 tube. The transformer also has two heater wires that run to the lamp and there are two what look like caps but could be resistors going to ground off each feed from the transformer. Two heater wires run down to the 12AX7's.
I will try and upload a picture but I think the site is not accepting them.
On the domino cap, the arrow side shows a black, red, violet (027) with a black,gold,black below which I guess means 27mmf?
The other cap is still a mystery.

[g1]

It also has some old caps I can't identify ...the second one is a brown cardboard covered cap with a marked positive end. It is labeled:
3 ohm Z 1-1/2V
12 45
K12U568 13

I would think it is some kind of combination component (cap with resistor in series or parallel?). Without a schematic it will be tough to figure what it is.

[JHow]

Couldn't "3 ohms" just be the ESR rating for an electrolytic cap? DId you try to measure the cap with a meter? What job was it doing in the circuit? Filter? Cathode bypass? Something else? You can probably figure out the needed value by knowing what it is supposed to do.

[davohilts]

The cap is bypassing a 2.7K resistor connected to pin one of the first 12AX7 tube. When I measure the capacitance I get 1940 mfd.
I don't know why there is no value embossed on the cap. There is a picture of the cap I posted a few replies back, if that will help.
Thanks!
Dave

[davohilts]

I have rebuilt the circuit board, following the existing layout. I have replaced the existing resistors and capacitors with new components and reconnected it into the circuit and simplified the grounding of components to limit ground loops. I installed a new 40x40x450V cap can I picked up from Hayseed Hamfest, checked all my solder connections and installed the tubes. The Tube Layout is as follows: V1 & 2-12AX7, V3 & 4-50L6, V5-35Z5GT.
I connected the amp to power thru a light bulb limiter and switched it on and it is up and running, however, I have a number of questions.
The wallpower enters the amp and the hot leg connects to the fuse, the neutral leg goes to the switch which is part of the tone pot. The switched leg continues to V3P7.
The power transformer has 5 wires. One wire connects to the fuse along with V5P2 at 120VAC. A second wire goes to V5P5 and measures 230VDC. One wire goes to ground. Two wires to to the Lamp, at the lamp 2-250 ohm resistors go to ground from each lamp pole and off these lamp poles wires extend to the heaters at V1 and V2 and measure 3.1VAC.
The amp functions and passes signal but I have an issue that i'm uncertain how to deal with. When I plug the amp in, the heater circuit comes on and the pilot lamp turns on. When the power switch is turned on (located on the tone pot) the amp then has B+ voltage at the caps and begins to pass signal. Is there a way that I can fully turn off power to the entire amp by making some wiring modifications? I will attach some diagrams of the circuit.
Thanks,
Dave

[nashvillebill]

Okay, here's some power supply basics. This is United States, 110 volt supply, correct?

You now have a 3 prong power cord. The green is ground. It connects to the chassis. The white is neutral. It should not be switched. The way you have the amp wired now, the amp is always on because white and green are connected internally in your breaker box, so the switch is doing nothing. Connect the wire from V3P7 directly to the incoming white wire.

The incoming hot (black) should be switched. The black wire connects to the fuse first--that part is correct--then it goes to one terminal of the switch on the tone knob. The other terminal of the switch goes to the wire you have labeled as V5P2 and the connection to the power transformer.

[davohilts]

thanks nashvillebill! I'll make the changes and report back. Someone put a 3 wire chord in this one use wirenuts and a bunch of stuff was disconnected. This is the first amp i've worked on with line voltages heaters and I was completely confused. Your advice gets my head back out of my your know what