Advise On Old 68 Rebuild

[Amp Kat]

Got this old Solarus or something like that, Sunn 68 model and the Power and output tranny are both toast. All original part's and two KT-88's and the 6AN8 allthough this one had a 7199 triode/pentode deal. Anyway the owner only plays this thing in church and loud just isn't in their vocabulary. Since I have to replace the tranny's anyway and volume is an issue I was thinking of turning it into a 6V6 with less plate voltage and a 5Y3 in liux of the GZ-34. My concerns are that phase inverter setup and what effects the lower voltage would have on the 7199 circuit as far as drive is concerned. What do you guys think ?

[Enzo]

KB, all those SUnns of that era are very similar. The amps with EL34s were nominally 40 watt amps while the more or less same model with a pair of KT88s was a 60 watt. You can tell which it originally used by the transformers. The output tranny was 3-40T, 3-60T, 3-120T, the number corresponding to the output power. so if it has an OT that is 3-40T, then it started life with EL34. If it has 3-60, then KT88s.

Same with power tranny. 3-4PT, 3-6PT, and 3-12PT. The 4,6,12 were paired with the 40,60,120 respectively. So if the amp has a 3-40T OT then it ought to have a 3-4PT PT.

The 6AN8 and 7199 were similar tubes, though the pinout differed. The 7199 was paired with the EL34, and ther 6AN8 was paired with the KT88s. SO if you have a 7199 circuit, but KT88s, I would bet someone stuck the KT88s in later in life.

The tranny numbers should tell the tale 7199 and 3-40 means EL34s.

If you intend to replace both trannies, I don't see why you couldn't make it appropriate for 6V6.

Since you are replacing the PT, The B+ is going to be whatever you make it. You can always alter the dropping resistors for the following B+ nodes to make them whatever you want. SO I see no reason the PI stages can't be at the original working voltages with little effort.

[Amp Kat]

Well thanks for the thourough insight and after further review of this amp it looks like it was allready altered because the OT is a Dynaco but I'll check the power tranny for some markings. The owner gave me some schematics and the amp had no power tubes so I'm not sure what was in it quite frankly. I agree and was thinking myself about what values I wanted to use for those dropping resistors. I'm thinking about around 380 volts or so for the 6V6's but wasnt' sure that was enough to drive that Pentode after the tone recovery and reverb recovery but I can get creative I guess if I have to. One other thing I saw on that schematic was it looked like the screens were sent to an Ultra -Linear tap on that OT. This schematic is for a 100s and doesn't say Solarus on it but I guess it's close enough. I wonder what the chances are of finding one of those OT ? They look pretty cool tstl.

[soundmasterg]

Many of the vintage Sunns did in fact use Dynaco transformers. The early 70's ones switched to Thoradson I believe. All the vintage Sunns used a UL connection on the OT. If you're going to be changing the transformers to go with 6V6's, I'd also change the phase inverter to some other circuit instead of the 7199/6AN8 cathodedyne setup. It isn't much more work to rewire that than what you are doing already, and you can redesign it to be better suited for use with the 6V6. A Deluxe Reverb uses 6V6's at about 430v, so you could probably raise your intended voltages a bit. You can get exact replacement transformers from Triode Electronics if you wanted to put it back to stock.

[Enzo]

The SOlarus and 100s are the same except for power amp and power supply. The 100s uses the KT88 and so uses the higher voltage/wattage power transformer as well. Larry has 100S on Schematic Heaven. EVen if the tranny says Dynaco, does it also have the Sunn part numbers?

I didn't look on Larry's, but on my 100S, the plate of the 6AN8 pentode floats. It should connect directly to the following triode grid as it does in the SOlarus.

The 100s had 25 more volts on the output plates and the PI ran on 385 instead of 300.

But as I said, it you are reworking it for 6V6, you can make the other B+ nodes whatever you want.

[Amp Kat]

Really appreciate the replies fellows and the OT only has Dynaco on it. Then again this thing is all gunked up as the black stuff came out the top and may have wiped it out but I'll try again and see what I can find. I do like the idea of that Deluxe PI and was kinda leaning towards that as you mentioned it SM.
Since I haven't heard one of these and it's looking like it's not going to be stock again what amp does it sound like ? Sure did like the idea of the Ultra-Linear taps but the new tranny won't have that feature unfortunately as it's going to be a Fender OT. Really don't want to deviate the circuit that much and may still keep the 7199 PI circuit and just put some screen resistors and let it roll. I'll keep you posted and see if I can find somemore numbers Enzo.

[Tom Phillips]

When you said

... the OT only has Dynaco on it. Then again this thing is all gunked up as the black stuff came out the top ...

it got me remembering that some of the old Dynaco transformers were really ugly looking even when they were new. I remember getting one that looked like it had been dipped in tar. It was "gunked up" when it was new. It too looked like black stuff came out the top. However, that stuff doesn't flow up hill. It looked like the big ugly black drops on top of mine were formed when the finished lamination stack was dipped and hung up to dry. So, are you sure both the PT & OT are toast because of the way they look or did you actually test them? Maybe you have a good one (or two). Seems unusual that both trannys would go bad in a Sunn. Could be some hidden gold there!

Regards,
Tom

[soundmasterg]

Stock, a Sunn sounds like itself and nothing else really. They make a great bass amp but I don't particularly like them for guitar myself unless I only want to play clean and want a different vibe than usual. If you're intent on modding it to use 6V6's, then you'll probably find that you won't like the preamp and PI circuit all that much. If it was mine and I was going to do the 6V6 and OT change, then I would definitly change the preamp and PI to something more suited to 6V6's. I would not attempt to run 6V6's with the stock PT as they would not even come close to holding to the 560+ volts in that circuit.

[Amp Kat]

Tom I did check both trannys and was hoping for some gold but the rainbow on the other end just wasn't true. The PS had a bad smell and only put out less than half and when powered down got hotter as time went by so I'm guessing it took a short in the primaries of some sort. The OT was legit from outside tap to tap but from CT to each side was open.

SM, I really appreciate that because I keep looking at that schematic wondering how this thing sounds because of the values and voicing I 'm having my doubts as well. I think I'll try to talk the owner into a AA763 Deluxe Reverb and just convert it over. Thanks for twisting my arm

[soundmasterg]

Yeah, theres lots of room in the chassis for a different circuit, and if you're starting from scratch and are intent on using this amp, then I'd probably just redesign it. If it were me though, I would probably just decide on a Webervst kit and go with that and restore this amp to stock and sell it. You figure a couple hundred for the transformers for this one, and a bit for the labor, and a Weber kit is around $400, and then whatever the labor is. The Weber stuff is very well thought out, uses good parts, and sounds very good. If you restore the Sunn to stock and sell it, you (or your customer) would be into a new amp for about the same money and it would be something purpose built that will have some value rather than a modded amp that may or may not have value. Anyway, my 2 cents.

[Boy Howdy]

I love my Sunns. I have a Sceptre and Solarus (both '69s). I use them for guitar. I did a thorough side by side with my restored '69 Bandmaster Reverb. Result: I sold the Fender. The Fender is better for strumming and probably for distortion (I use my Sunns clean only), but the Sunns work much better for my playing style. Overall, the Sunn's bright channel sound was very similar to the Fender (it could just about duplicate it exactly), but with a slightly stouter midrange.

Yes, restore that puppy. And give me a call.