Magnatone 280 B built, vibrato questions

[dinkotom]

Hi folks,
I just finished building a Magnatone 280B model, it works fine, but I somehow expected a bit stronger vibrato - if I compare it to Robert Ward's or Lonnie Mack's old records it's still not quite there, but I guess I might be setting my hopes too high . I'll send some clips soon so you can hear it.
So, could anything simple be done to make intensity function stronger - like change value of some resistors/caps or intensity pot? Before I begin my usual trial and error (mostly error, I'm afraid) way of doing things, I'd rather hear some useful suggestions from more knowledgeable folks here.
Here is a schematic for 280A model (a bit different, but the vibrato section is the same):
http://www.schematicheaven.com/barga...atone_280a.pdf
Regards,
Dinko

[dinkotom]

I guess I should have started this thread in "Mods & Tweeks" section, please move it there if possible.

[capnjuan]

Hi dinkotom; congratulations on your build. Don't know much about the amp other than those varistors are what make the vibrato run. Are you sure you have the right ones? If, yes - other people might like to know where you got them and any technical specs you have on them. CJ

[dinkotom]

Hi CJ, varistors are Workman FS 1226 (blue tubular), were available at Talonix.com until a couple of months ago, sadly no more The amp sounds very much like the real Maggie, though as I said, maybe not 100% quite there, might be the some other things beside the varistors.
Here are some clips of a previous Magnatone amp I made, model 213 - the varistors in it are Workman FS 1205 (these look like the ones Magnatone used, brown tubular), but, to me, vibrato on this amp sounds about the same as on the 280B (of course, except when 280B model is switched to stereo mode,then it sounds more like a chorus), so your ears be the judge
YouTube - Magnatone 213 homebrew testing (jazzmaster)
YouTube - Magnatone 213 homebrew - solo from Midnight at the oasis
YouTube - Magnatone 213 homebrew testing - afro noodling

[capnjuan]

Good stuff dinkotom and congratulations again on your Maggie build. Too bad about the varistors ... it was always just of matter of time. In the last year or so, I've considered a couple of 1/2-dead Maggies but couldn't get past the parts issue. Wish I had more to help with on the circuit. CJ

[dinkotom]

CJ, you got PM!

[dinkotom]

.. in the meantime I rewired an old Twin-wreck into a Magnatone 260 and this thing has that mad, over-the-top-gurgle Ward/Mack vibrato I expected to get from 280 model!

So, can anyone tell me if the 260 model is supposed to have so much stronger vibrato than 280? 280 sounds good too, but it's nowhere near the 260 vibe. I did try different varistors, tubes, caps, resistor values - no change in vibrato. So maybe it's supposed so sound as it is.

I also replaced all 820pf (attached to varistors) caps with 1nf - and vibrato seems stronger now!? Does this make any sense?

Checked the voltages, some are off - instead of 58V on the grids of V7 (12BH7) I measured 24V. On pin 3 of the V6 tube - instead of minus 2V I get minus 0.6V. Tried different cathode (820 and 470 Ohms) and plate (470K, 100K) resistor values on V6 and the voltage is the same - minus 0.6V !? Swapped tubes - no change.

Any thoughts?