K-502 Help

[czucker]

Hi folks,
A few years back I put together a K-502 tube amp kit from tubesandmore.com.

Two of my resistors recently burnt out. I can't read the bands on them and they're dead to my multimeter.

Does anyone have the wiring diagram for this handy? Or can anyone tell me the resistor values?

The ones that burn out are towards the front of the board, near the RCA input jacks. They are significantly bigger than most others on the board and they're blue.

Here is a picture with the resistors boxed in red.

Any help would be greatly appreciated.

Thanks,
Chris

[Matt.B.H.]

Hello Chris,
Was the picture taken before they burnt out? I tried zooming in but the res. is too low for me to see the bands. If you have a high res. copy of the pic. you could tell from that.
If not can you trace out where they are in the circuit from the board.
Cheers Matt

[HollowState]

Originally posted by czucker
A few years back I put together a K-502 tube amp kit from tubesandmore.com.

The kit sold by Antique Electric used 11BM8s instead of 11MS8s. I believe the resistors you're having trouble with are the common cathode resistors for the PP pentode output stages. See the picture link below. They will be fairly low values. The ones in the picture below look to be around 100-200 ohms/2 watts or better. This is just a guess!

http://nullspace.us/11bm8/mills&auricap.jpg

[Matt.B.H.]

Hi HollowState,
I thought they may be common cathode resistors maybe 100R.
Chris you could try contacting S5 Electronics. They apparently made the kit for Antique Electric.

http://www.s5electronics.com/

Cheers Matt

[czucker]

Hi Matt,
Thanks for the reply. Unfortunately that picture isn't even of my board. I don't have a good picture from before they burned out.

I'm very much a beginner here. I am just hoping someone else who has built this kit is lurking around here somewhere.

Best,
Chris

[czucker]

This image from a K-12M may be clearer. . .

http://gallery.me.com/chris.zucker/1...12476863090001

[Matt.B.H.]

Hmm, this is a guess but the bottom one in the photo looks to be red, black, brown= 200R. Also there could be a reason they let the smoke out. I would make sure your power supply is ok as both went and the PS is common to both. Did they both go at the same time or was it a gradual thing? ie they ran hot anyway. Seems odd that they are both open though.
Cheers Matt.

[HollowState]

Originally posted by Matt.B.H.
Hmm, this is a guess but the bottom one in the photo looks to be red, black, brown= 200R. Also there could be a reason they let the smoke out. Seems odd that they are both open though.

I was thinking maybe red-black-brown also. Difficult to be sure in these pictures. They also look like they're possibily metal film resistors. If so, this could explain why they went. MFs can't take any overload, even momentarily.

[Matt.B.H.]

Yes I thought that, may be deliberate (I cant spell) to act as fuses. They do look cementish though maybe metal oxide, even still must have been something to make em both go. Maybe Chris was belting it out and they both just lost the will to live

[DigitalJunkie]

I just found this snippet:

I was checking out a batch of used and NOS 11BM8s this weekend, in one of the upgraded K-502 amps, and found one used and one NOS tube that would get into a "bias runaway" condition after a few minutes operation, the normal voltage drop across the 200 ohm resistor, for a pair, is about 14-15 VDC representing 70-75 mA for a pair.

From:
http://www.diytube.com/phpBB2/viewto...492de5cafc85ec


This seems to state that they are indeed 200ohms. (atleast for the 11BM8 version) Looking at the Pics,that would have been my best guess also.