Magnatone Varsity M-197-3-V

[Resonator Guy]

Gentlemen, I am currently working on a Magnatone Varsity M-197-3-V amp and cannot find anything resembling a schematic. There is a wafer capacitor between pins 3 and 6 of the 6V6 and a large resistor between pin 8 of the 5Y3 and pin 6 of the 6V6. Does anyone have an idea of the approximate value of these so I can try and get this to stop distorting. I have made considerable headway replacing parts I can read, but these two have me stumped. Thanks

[nosaj]

Gentlemen, I am currently working on a Magnatone Varsity M-197-3-V amp and cannot find anything resembling a schematic. There is a wafer capacitor between pins 3 and 8 of the 6V6 and a large resistor between pin 8 of the 5Y3 and pin 6 of the 6V6. Does anyone have an idea of the approximate value of these so I can try and get this to stop distorting. I have made considerable headway replacing parts I can read, but these two have me stumped. Thanks[ATTACH=CONFIG]35076[/ATTACH][ATTACH=CONFIG]35077[/ATTACH][ATTACH=CONFIG]35078[/ATTACH]

You'd be best off replacing the paper caps first then worrying about the ceramic last . The large resistor is it open?

nosaj

[Resonator Guy]

I replaced the paper caps earlier. I am enquiring about the two items that I cannot read values on. I do not know if the resistor is open or drifted or what. I am seeking a replacement value for it and the disc or wafer cap as described.

[guitician]

That ceramic tube wirewound may be 500 ohms like a tweed Princeton uses. The ceramic disc could be .001uf 1KV, .005 500V. Pin 8 on the 6V6 is used as a terminal point, no connection to the tube.

Is that a 470K plate load resistor on the first tube? That will sure distort some signal if it is not a very low level.

[nosaj]

I replaced the paper caps earlier. I am enquiring about the two items that I cannot read values on. I do not know if the resistor is open or drifted or what. I am seeking a replacement value for it and the disc or wafer cap as described.

If you do not know if it is open, drifted or what why replace it. Use a meter to see if it has a problem it is not likely to drift. How about some new pics ?

nosaj

[Resonator Guy]

A mistyping on my part. The cap is between pin 3 and 6 of the 6V6.

[Resonator Guy]

If I lift one end to use a meter on it and I do not know what it should read, then I can not tell if it has drifted. It is not open because the amp works.

[eschertron]

So what does the value of the resistor read? 470R or so is ballpark for the cathode resistor. Let us know where pin 6 goes, is it grounded? That's my suspicion.

The cap (anode-cathode) is a bit funnier. What does it measure? My champ has a 330pF cap grid to cathode to prevent parasitic oscillation. If the distortion you are hearing is HF noise bursts, I'd suspect something like that is the intended function.

If you've replaced (many of) the parts you can ID, then you must have a fairly complete schem of this beast by now. Do share

edit (simulpost): The cap is anode to ground. That can only reduce the impedance at higher frequencies. This is the output tube, correct?

[guitician]

A mistype on my part, pin 6 is unused on the 6V6, not 8...

[Resonator Guy]

Folks, I was given this link at another site. https://l.facebook.com/l.php?u=http%...df&h=dAQGCygy9 . The schematic bears no resemblance to what has been done to my amp. Based on the soldering etc, I believe someone has heavily modified this one at some point, and now I need to think about rescuing it as it is or tearing it down and rebuilding it as it originally was. My head is starting to hurt. By the way, that big resistor measured 1K. The schem shows a more recognizable wiring method including biasing the 6V6. I have to do some deep thinking over a glass or two of wine. Thanks for getting me thinking that I should not just be replacing parts. I would rather make it correctly.

[guitician]

I see so the .01uf disc and the 1K 10W meet at pin 6 of the 6V6, with the OT lead. And it uses a 500k plate load(470k), not too big for a single pentode I guess.

[52 Bill]

Please double check the pin numbers on the 6V6 or at least tell us what else connects to the pins that the cap and the resistor connects to.

The large resistor looks like it should be the first power supply dropping resistor coming from the rectifier tube, which I would expect to be connected to the screen of the 6V6.

Maybe a better photo of the 6v6 tube socket.

[eschertron]

Thanks for getting me thinking that I should not just be replacing parts. I would rather make it correctly.

Rebuilding from scratch (or semi-scratch) would be a fun project, and let you hear the original intent of the design. After that, you might be able to apply some informed choice on modifying the amp to explore and learn. If it's been hacked to the point where it doesn't work right now then possibly the last person who worked on it overstepped their theoretical knowledge boundaries!

[Enzo]

So you have a cap and resistor in series - call it RC. RC is wired between the plate of the 6V6 power tube, and B+. Sounds to me like it is across the OT primary, parallel with it. Sounds like a little conjunctive filter to me.

[Resonator Guy]

I will post some better pictures today (if I can take better pics) so you can perhaps tell what is going on. I am almost sure I will strip stuff out and rebuild it to the original schematic.