Sunn A212 Questions

[mckinnon audio]

  Hi there,you can see from the photos that your two 8 ohm spkrs. are hooked up in parallel,giving you a 4 ohm load which matches your trans.I'd say it's a little light in the power rating but it'll prob.work for quite some time.If it was mine I'd look for an orig. trans.if I was going to use it a lot,good luck Mel.

[biltmore]

I'm always on eBay and I never see original output transformers (taken from Sunn amps) on there. Can you suggest another transformer that would be better? I'm definitely going to be using this amplifier a lot, so I want to make sure that everything is in top shape.

[mckinnon audio]

  I've had great success with trans.from Mercury Magnetics,a bit pricey but worth every penny.I don't know if they make an A212 model.You could try Hammond Trans.also,they would be cheaper,hope this works out for you,Mel.

[biltmore]

Is there anyway to get the specs for the output transformer that I need from this schematic? This stuff is like greek to me.

http://www.el34world.com/charts/Schematics/Sunn_MODEL_A.pdf

[mckinnon audio]

  Hi there,basically what you need is a 60 watt output trans. with ultralinear taps.On the schematic these are the 2 windings that go to the screens,(dotted line inside tube).There's also 525 vdc on your center tap,so look for one that's insulated for 600 vdc or more,good luck,Mel.

[biltmore]

Thanks for the info Mel. I'm going to look around and see what I can find. I definitely want to try and bring it up to vintage spec as much as I can.

I have a couple of new questions.

Is having the 4ohm transformer in there just bad in general, since the Model A is an 8ohm amp?

My reverb is acting up. In Channel 1, it's okay in both high and lo outputs. In Channel 2 tho, it breaks up and distorts on both high and lo outputs. If I have my guitar in channel 2, and I have the reverb selected for channel 1 ... if I turn that knob up, it gives a crazy high pitch feedback. I remember that you mentioned that there is a 22V zener diode that regulates the voltage that powers the reverb and biases the preamp that needs to be taken into account when installing a bias pot. Could that have something to do with it?

[loudthud]

On CH2 there is a gain switch (low, normal, distort). If it's in the Distort position, I think the reverb is going to be distorted. If it seems to work correctly in CH1, I would think the -22 is working correctly.

[biltmore]

The gain switch set at low produces a lot of gain and hardly any reverb when you turn the reverb effect up. The gain switch set at normal produces distortion when you turn the reverb effect up.

It was working a couple of weeks back, so something's definitely up.

[biltmore]

Well since nobody has any ideas as to why this funky issue is happening with my reverb, I guess I'll just have to cross my fingers and bring the amp into Amphead and see what's up. Hopefully it's nothing too bad. Oh, and I still haven't heard back from Mercury Magnetics about putting together a new transformer for me, but it's probably because everyone's off for the holidays.

[gregovertone]

what about this one?

http://cgi.ebay.com/P782-S-Dynaco-MK3-MK-Mark-3-2-Sunn-Power-Transformer-Nu_W0QQitemZ200133157601QQihZ010QQcategoryZ67815QQssPageNameZWD1VQQrdZ1QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247
 

[biltmore]

Holy shit Greg!!!!!! How in the world did you find that?!

I also found the transformer on their website too, so I could bookmark it.

http://store.triodestore.com/mq782.html

Mel, is this a suitable replacement? I have no idea if the specs match up or not, as that stuff looks like gibberish to me. I wonder if Triode Electronics is as dependable as Heyboer or Mercury Magnetics.

As soon as I get a "yeah, it's good to go" ... I'm buying. If this is the replacement that I need, then I can take it into Amphead and replace the old one and get my reverb checked out at the same time, which will save me some $$$.

[mckinnon audio]

  Hi there,it looks like it will work,you don't need the 5 V htr. winding and you'll probably have to fool around with the bias supply resistors to get the volts right,maybe not.I guess all that matters is that you have the Dynaco trans.,by the sounds of things if it's the Schumacher trans.,it won't work,or they don't recommend it.Good luck,Mel.

[biltmore]

Hey Mel (or anybody else that can help), there's some crazy thing going on with my amp. When I turn it on, I always turn the channel and volume knobs down to 0. Within the first 5 minutes of warming up, it makes a crackling sound ... like there's a scratchy pot. Then after it makes that sound, it never comes back. Do you have any idea as to what could be causing that? Bad preamp tube or something?

[mckinnon audio]

  Hi there,sounds like it could be a tube,try cleaning the tube sockets and the tube pins themselves. I'd check my cathode caps also,and the bias cap/circuit.Good luck,Mel.