The sunn Forum
Sunn Musical Equipment => Q & A => Topic started by: biltmore on October 25, 2008, 02:19:37 pm
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Hello everyone, first poster here. It's great to see a forum dedicated to Sunn, and it's even greater to see Conrad himself posting on here. To me, he's a legend ... and then some. I absolutely can't thank Conrad and all the other old Sunn employees enough for making such great amplifiers. Over the years I bought quite a few Sunn amps, an early Model T, alpha 212r, alpha 112pr, and a beta lead head.
I recently added another member to the family, this wonderful Sunn A212:
Front
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20Forum/Front.jpg)
Back
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20Forum/Back.jpg)
Speaker
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20Forum/Speaker.jpg)
I'm in love with the off-white tolex, and whoever put it on did a pretty good job. I found a picture of an A212 with the original tolex ...
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20Forum/SunnA212.jpg)
And as much as I adore the old black Sunn tolex, I just can't bring myself to take off the off-white tolex.
For those who don't know much about this amp, it's powered by 2 x 6550's, the preamp is powered by 3 x 12AX7's, and the reverb is powered by 1 x 12AX7. The speakers are 2 x 12" Sunn Transducers (128G-SP).
Front of the amp:
Channel One
* Hi & Lo inputs
* Volume, Bass, and Treble controls
* Hi Boost switch
Channel Two
* Hi & Lo inputs
* 3 position gain switch (Lo, Norm, Distort)
* Hi Boost switch
* Volume, Bass, Mid, and Treble controls
* Mid Freq. Select switch - 705 / 1.5K / 3K
* Reverb channel selector switch - CH1, CH2, Both
* Reverb level control
* Master Volume control
Also located on the front panel is the On/Off Standby and Power switches.
Back of the amp:
* Polarity switch
* Circuit breaker (rated at 4.5A)
* 120V 60Hz 250W 3-Prong Power Cable
* Accessory 3-Prong connection (120V, 60Hz, 400W MAX)
* Reverb Footswitch input
* 600 ohm out
* Speaker outputs, 1 is capped, 2 is open (110 watts max)
And that about does it for the details.
Questions
The amp was recently serviced here in Portland at Amphead, and the tubes were purchased at Eurotubes here in town. It's currently packing 2 new J.J. KT88's and 4 new J.J. 12AX7's. I read on here that the amp is based on Sunn's traditional 2x6550 60 watt amp, but I've also read that the 2 6550 tubes are run in a "push-pull" mode for a total of 100 watts RMS. I'm curious as to what watts this thing is really pushing, as it feels more than 60 watts when I open it up. Is this 100 watts RMS thing true? It just sounds odd to me as I know that the Model T uses 4 6550's and puts out 150 watts RMS. Also, is it okay to have KT88's in there, instead of having 6550's?
I'm curious about the polarity switch on the back of the amp. At the moment, it's currently facing down and the amp is operating well. When I went over to a friends house yesterday we moved it up, and the amp started giving off a weird feedback, so I immediately turned it off and flipped the switch back downwards. Forgive my newbie-ness and please tell me what the polarity switch is used for, and if I have it in the correct setting.
The guy that I bought the amp from told me that when he was having it serviced at Amphead, the guy (Jim's his name I think) said that the standby switch was broken, but apparently it's not a real standby switch as it doesn't idle the current. It's nothing more than a mute switch, which I found to be odd. Is this common on any other Sunn's? And while working on the amp, Jim added an internal bias pot, which I thought was pretty cool. Where some people would remove it to bring the amp back to its vintage specs, I'm not planning on doing such a thing because I believe it's practical thing to have.
All in all, I'm very pleased with this amp. I know it's Sunn's answer to the Fender Twin Reverb, and in my opinion, it knocks it out of the water. It has a more pleasing mid to low tone, and the Mid Frequency Select options are just amazing. You can dial in all sorts of tones, all the way from twangy to stoner/doom rock. It's a versatile amp, and I'm lucky to own one. I don't see these often, and I wonder how long they were manufactured. It seems that most people on here say that they're from 1973/1974, but sadly there's no official documentation that I've seen that states what amp this year was made in. The guy that I bought it from said that it was a 1974, and was told that by the guy that he had bought amp. I'm curious if Conrad or anyone else here can dig up the information on this amp.
Also, I feel like the Hi Boost switch doesn't do much, could it be that it's broken?
And for my last inquiry, it says SUNN Model A on the back. Was there any other Model A series amps, or was this it? I've read on here that the preamp is similar to that in the Model T, and I'm curious to see what else this amp borrows from other Sunns.
I really wish that there was a larger and more extensive catalogue for finding out information on old Sunn amps, but it's great to see that you guys have the Sunn Museum up and are adding information to it. I can only hope that we get more models and information added to it so that we can preserve Sunn's history as much as we can. I know that we're not getting any younger, and it pains me to think of all the valuable information that's out there in the minds of former Sunn employees.
If you made it all the way down to here, thanks for reading.
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There is a schematic of the Model A in Aspen Pittman's book and you can find it online here:
http://www.el34world.com/charts/Schematics/Sunn_MODEL_A.pdf
The schematic is dated 9-14-74 so that's around the time it came out. It's not in the 74 catalog. The preamp is kinda like the 2nd gen Model T with James type tone controls and the inductor midrange on CH-2 but there is an unusual biasing scheme for the preamp tubes and a JFET on the input to CH-2. The High Boost on CH-2 will only give about a 3dB boost, different from CH-1.
The schematic shows a three wire line cord. Back in the days before 3 wire outlets were standard power wiring in the US, the polarity switch was used to reduce hum from guitars and give a path to ground for leakage currents. It really doesn't do much if the 3 wire feature is working properly.
It's not easy to get 100W out of a pair of 6550's. The Model A uses an Ultra-linear connection for the screen grids so it's probably about 75W. KT88's should work fine if the bias is adjusted for them. I hope your tech had a schematic and didn't just install a bias pot willy-nilly. 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.
The standby switch is just a mute. The Enforcer used the same type standby. Your switch probably just needs a good shot of contact cleaner. There is a replacement switch that will fit but it's not an exact replacement. Search the forum for posts by me for a Model T power switch.
It would be nice to have a better picture of the chassis where the tubes are. Could you remove the back board and shine some light in there?
No telling what the weird noise was. Next time it happends, turn down the master volume. Could just be a bad preamp tube. It has nothing to do with the polarity switch.
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Thanks for all the info loudthud!
Looks like 1974 was the year that these guys first came out, according to the schematic. Sweet. I wonder how long they stayed in production and how many were made. Of the 5 A212s that I've seen, everyone of them had a serial number starting with 50 (50XXX).
I mainly play in CH2, so maybe that's the reason why I'm not hearing a huge difference with the Hi Boost switched on.
I guess the polarity switch is fine where it is then, since the amp's working just fine with it switched down.
I'm pretty sure that Amphead has a schematic of the Model A as they work on a lot of Sunn amps, so I'm willing to bet that he did a good job with it. Still, I'm going to call him today and make sure that he took the 22V zener diode into account. You never can be too cautious. I'm also going to ask him if the standby switch is dead, because if it only needed a cleansing I would think that he would've taken care of that. I *might* get it replaced, but since it's nothing more than a mute, I can just turn the volume knobs down. Thanks for the heads up on the replacement switch.
I'll get a nice shot of the chassis later on today for you.
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Wow, great information! I'm also a first-time poster and am REALLY glad to have found this forum.
I just picked up a Model A myself.... my first Sunn. :-D As you can see, it doesn't have a baffle board. I'm looking to get a replacement board made and am curious about these little plastic nub pieces that must have locked the board on like a couple of Lego pieces. I've never seen this before. Are they standard on Sunns??
(http://i154.photobucket.com/albums/s251/MisterTV/SunnmodelAfront.jpg)
(http://i154.photobucket.com/albums/s251/MisterTV/Sunnampbaffleconnector.jpg)
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Hi there,yeah they're orig.You see them on the 70's amps,not too much on the late 60's ones.You just banged the grill board with your fist and it snapped right in.Nice amp by the way,good luck Mel.
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Good to know, thanks. Is it possible to find these fasterners anwhere? Or would I have more luck tracking down a Bigfoot? :-) I'm not keen on the notion of drilling holes to screw in a replacement baffle, so even an idea for something similar that I might be able to pick up at Home Depot would be greatly appreciated!
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Looks like you've got yourself one nice A212 there MisterTV! Sweet! What a nice introduction to Sunn.
I totally need to get that chassis shot up on here. I forgot all about that.
As far as the fasteners go, I have no idea where you'd find them. I don't even know what they're called. Hopefully someone here can fill you in on this. Sucks that the board is missing. I wonder what the story is with that.
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i have several sunn cabs with these types of fasteners. and i just removed them and stapled some regular velcro in the same spot. works just fine.
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As a new guy around these parts, are there some DIY forumites I could contact about having a replacement grill cloth frame made for this? (With grill cloth attached, of course!)
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It would be nice to have a better picture of the chassis where the tubes are. Could you remove the back board and shine some light in there?
I finally got around to opening up the back board and taking some pictures. Hopefully these will satisfy! BTW, these pictures are all taken from left to right ... and sorry for some of the blurriness, my camera is a piece of crap.
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/1.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/2.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/3.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/4.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/5.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/6.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/7.jpg)
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i have several sunn cabs with these types of fasteners. and i just removed them and stapled some regular velcro in the same spot. works just fine.
That's a wonderful idea. Some of my fasteners are pretty old and brittle, and I just might end up going the velcro route in the near future.
As a new guy around these parts, are there some DIY forumites I could contact about having a replacement grill cloth frame made for this? (With grill cloth attached, of course!)
Just to finish this up, MisterTV contacted me via email and found someone to build the grill frame for him online. I provided the measurements for him, so if anybody needs them in the near future ... just ask.
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Hi there,the chassis looks like it's in really good shape,you should try to get some tube shields for your preamp tubes,where they hang upside down they'll keep them tighter in the sockets.The output trans.doesn't look right to me,different cutout in the chassis and it looks a little small for a 60 watt output trans.Anyone else got any thoughts about this ?
Still a nice amp though,good luck Mel.
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Hi there,the chassis looks like it's in really good shape,you should try to get some tube shields for your preamp tubes,where they hang upside down they'll keep them tighter in the sockets.The output trans.doesn't look right to me,different cutout in the chassis and it looks a little small for a 60 watt output trans.Anyone else got any thoughts about this ?
Still a nice amp though,good luck Mel.
I've got the original tube shields, they weren't on when I bought the amp. Good thinking tho, I'll definitely throw them back on there.
About the Output Transformer, I thought the same exact thing Mel. It has to be a replacement, since there's that space around it and there's 4 holes. I'll get some information off of the sticker on the Transformer, and see if we can find out what's up with it.
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Hey Mel, this is all the information that I could get off of the Output Transformer ... it's off of the sticker that you can see in the photos.
TF-127
T540918
10520209
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I did a google search for "TF-127 Output Transformer", and I found a couple of links:
http://www.magicparts.com/new/transformers.htm
According to MagicParts, here's the scoop on what the TF-127 is:
TF127 Fender Pro Reverb, 2 X 6L6GC - Output Transformer Bandmaster 4ohm output Mounting Centers: 3 9ΒΌ16"
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On Vibroworld, it says the same thing essentially .. with a little more info:
TF127 - Fender Pro Reverb, Bandmaster, Tremolux - 2 x 6L6GC - Speaker output Transformer 4-ohm, Hole mounts 3.50-inches center-center. Primary resistance: 20,000-ohms; secondary: 4-ohms; Frequency response: 20Hz to 20kHz.
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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.
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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.
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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.
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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
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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.
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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?
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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.
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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.
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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.
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what about this one?
http://cgi.ebay.com/P782-S-Dynaco-MK3-MK-Mark-3-2-Sunn-Power-Transformer-Nu_W0QQitemZ200133157601QQihZ010QQcategoryZ67815QQssPageNameZWD1VQQrdZ1QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247
:-D
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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 $$$.
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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.
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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?
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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.
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that p782 is what I replaced my 200s with. works great in there. if you are replacing/upgrading the transformer, replace the caps. I didn't see anybody mention that. really, get it to a good amp tech that knows tubes and salavates when he sees your amp(that's how you know he knows tubes) and for $200 plu parts, your amp will be tip top. unless you have time and a lot of knowledge and experience behind you, take it to a pro. you'll be happy, the economy grows and your Sunn has the best chance of living.
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I don't know if you have had the amp serviced yet, but I recently had my Solarus overhauled by Jim at AmpHead and I couldn't have been happier with it. So far every amp I have taken to him has been fixed right the first time.
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djc, thanks so much for sharing that info with me!!! I really appreciate it. I'm just about ready to buy the transformer, and am really happy that it's only $104.95 ... instead of $350. And thanks for the recommendation on replacing the caps along with the transformer. I'll be taking it to a place here in Portland that specializes in fixing Sunn amps, it's called 'Amphead'.
volvoguy27, I'm actually taking it in to Amphead here soon. It had been serviced there before just before I bought it. I've heard great things about them from quite a few people, and apparently they have the A212 schematic there too, which is a bonus. Still, thanks for the recommendation!
Thanks for looking out guys! Really appreciate it. This A212 is quite possibly my favorite amp of all time.
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my buddy, jeremy hooton, re covered that amp. it used to be owned by a mutual friend of ours.
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Jeremy of the Portland Custom Shop?
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yeah, thats the dude.
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Mel, or any of the wise ones ... is this the right Output Transformer for my A212? I need to buy this thing a.s.a.p.
http://store.triodestore.com/a4dyoutr43oh.html
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Hi there,yes I'd say that should work fine for you.Let us know how you make out with the install,Mel.
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Thanks a ton Mel!! I'll let you know how it goes. Really excited to see how this is going to turn out.
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I got my amp back from Soursound / Portland Custom Shop yesterday, and everything went well! Apparently what caused my amp to trip its breaker and smoke, was a shorted out KT88. It blew my Hum inverter or Hum _______. I guess a couple of the resistors blew, and Bryan fixed it to where it shouldn't happen again. The reverb tank was also replaced with something much much better, and the opamp for the reverb was replaced too ... and the reverb sounds freaking amazing now. Really deep and lush, without any strange high end noise. He also mounted the reverb unit on the bottom of the amp, instead of being mounted on the back panel ... as it yielded a lot less noise that way. I never knew that the reverb tank's position in comparison to the amp made that much difference, but it did! I have new JJ KT88's in there, and that brand new Triode (Dynaco) replacement output transformer. The transformer is a standup, and he could've done some custom work to the transformer to make it lay down, but the easiest way to mount it was in a standing up position. He only needed to drill a couple of holes, and do some stuff to increase the strength of the clips. He was saying how most of the new transformers he gets all need a decent break in time, so I'm guessing that even tho my amp sounds alright now, it's only going to get better.
Here's some pics!
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3556.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3554.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3555.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3557.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3558-1.jpg)
(http://i64.photobucket.com/albums/h179/dead_red_eyes/Sunn%20A212/DSCN3564.jpg)