The sunn Forum
Sunn Musical Equipment => Q & A => Topic started by: Jenkster on February 09, 2008, 02:10:30 pm
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Hi all, newbie to the forum looking for information. I have an opportunity to buy a 1965 SUNN head for $400 locally. It is in great shape cosmetically save for a small tear in the grill cloth. The pre-amp and rectifier tubes look original, the two 6550's have been replaced. It has a hum and plays at very low volume. Can't seem to find much information on this year of SUNN amp. Is it likely one the brothers built in their garage? Any information would be appreciated.
Thanks
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A picture would help immensely. How do you know it's from 1965?
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The funny thing is the seller had this amp listed on the local Craigslist earlier today with four very poor quality pictures. I just looked for the ad again and it's gone. I have an appointment to see it tomorrow morning. The seller told me it's from 1965. He said the amp section is a Dynaco and it has a sun with a smiley face for a logo. He claims everything is original save for the power tubes. If the caps are original, I'm sure that is part of the sound problems. Any definitive way to tell the year of manufacture?
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I think the top control, split chassis amps are prior to '67, smiley face logo '65.
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If it is a 65 and in the condition the seller claims, it is worth $400 to me. I could tell in his pictures that it has top controls and probably a split chassis. I let my 74 Model T go a few years ago and have regretted it ever since! If I do get it, I will be sure and post pictures. Thanks EdBass for the info!
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If it's a top control, it's a split chassis. As a rule, I don't speculate on vintage equipment value, I'm a firm believer that used gear is worth exactly what someone is actually willing to pay for it, "opinions" are worthless. I have absolutely no use for the opinion of someone without "skin in the game".
That being said; I would pay $400 for that amp as described, without hesitation.
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I picked up the amp today and it appears to be original. I am having difficulty posting pictures. I'm not too computer literate! I do have a couple of questions. There appears to have been something mounted inside the cabinet on the lower right side looking at the back. It would have been approx. 6" long and 3" wide attached with four screws. The seller said there was nothing there when he aquired it. Also, for schematic puposes, can someone tell me the model of the Dynaco amp they used?
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A friend of mine and I fired it up and it had a very loud HUM! Volume didn't change the level so we figured it had a ground loop. We pulled the amp and found someone did a hack job on it. The bias cap was gone, the resistor accross the pre-amp power socket was gone, there were other gounding and wiring issues as well. The GZ-34 rectifier tube was replaced with a 5U4 and there was a bad pre-amp tube, a 12AT7 instead of a 12AX7! I think that's it. Oh, the amp power cord was replaced and instead of a 3 amp fuse it had a 32 volt 4 amp fuse! I'm not quite sure how it worked at all???
We did cure the hum but the volume is too low? It blew the the 3 amp 250 volt fuse we put in after about 10 minutes of operation. It is certainly a work in progress! For the time it did play, it was very, very clean!
The pots and filter caps are dated Jan/Feb of 1966. The pre-amp housing was obviously "home made" by the uneven sharp cuts on the aluminum sheeting. Looks like they used tin snips or something similar to cut it, how cool is that! The pre-amp appears to have been un-touched inside. Sure was a pain in the a** getting it out of the cabinet! Pots are noise free which is a good thing.
I am still trying to reduce the resolution of my pictures but have had no success. Hopefully I can get my daughter to help me with that in a couple of days.
Any input would be appreciated!
Thanks,
Mark
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I suppose it would be an exercise in futility locating a schematic for the pre-amp? If anyone knows the type of screw-in bulb it takes, that would be helpful.
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I suppose it would be an exercise in futility locating a schematic for the pre-amp? If anyone knows the type of screw-in bulb it takes, that would be helpful.
Psst... sell it to EdBass!!!
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I picked up the amp today and it appears to be original. I am having difficulty posting pictures. I'm not too computer literate! I do have a couple of questions. There appears to have been something mounted inside the cabinet on the lower right side looking at the back. It would have been approx. 6" long and 3" wide attached with four screws. The seller said there was nothing there when he aquired it. Also, for schematic puposes, can someone tell me the model of the Dynaco amp they used?
It's a Dynaco Mk III (KT88/6550) or Mk IV (EL34) power amp and a (mostly) PAM preamp. I wasn't aware that Sunn amps that old had a reverb tank, but that could explain the "missing piece". Do the controls make any mention of reverb?
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I suppose it would be an exercise in futility locating a schematic for the pre-amp? If anyone knows the type of screw-in bulb it takes, that would be helpful.
Psst... sell it to EdBass!!!
I assume you are being smug Joe :roll:. All kidding aside, I would be a player if it's not too hacked up. It's not like they are making any more of them. :wink:
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Thanks for the reply. I did figure out it was a Dynaco Mark III and matching pre-amp. There were issues with the amp that have mostly been cured. Naturally I have kept anything that was removed. Whovever worked on it before removed the bias cap but didn't replace it? That was just one issue. No indication of reverb just the volume, bass and treble pots, high, low, standby and power switch, single 1/4" input. Since I can't seem to reduce the resolution of my pictures, I may be able to e-mail them to someone if interested in checking it out. At this time, it is not for sale.
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I suppose it would be an exercise in futility locating a schematic for the pre-amp? If anyone knows the type of screw-in bulb it takes, that would be helpful.
Psst... sell it to EdBass!!!
I assume you are being smug Joe :roll:. All kidding aside, I would be a player if it's not too hacked up. It's not like they are making any more of them. :wink:
Nope, I never "be smug". I can't even think of how I would start! :-D
Yep, they are not making any more of a lot of things... :lol: :lol:
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Pics I hope!
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Another!
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#3, Here you can seen the clean spot on the right side where something was mounted???
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#4, Better view!
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#5
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Last one! Thanks to my daughter for her help!!!
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wow i've never actually seen a real dynaco.
i bet you it would sound AMAZING if you plugged a record player into it. :D
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That is a true classic amp. So glad to hear you are restoring it and appreciate it's value both as a piece of history and as a fabulous amp.
Thanks your daughter for us as well. Yeah, I need to ask my son how to do some stuff on my computer....what happened to me being the smart one?
No, I did that stuff a long time ago.........
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Here is a shot of what the Sunn Badge and knobs should look like. The jack by the boost switches is not original. The Badge is from the first run of amps. I have seen examples of amps like yours with the newer non-(R) badge but that may not have been original. There is a schematic here:
http://sunn.ampage.org/site/schematics/mod60.jpg
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Thanks for the info and pic loudthud, I appreciate it! The input jack not being original makes sense now. I suspected the missing piece in the rear of the cabinet may have been the original input(s) box. Looking inside the pre-amp, the top input was obviously wired differently than the rest of the pre. Would you happen to have a picture of the rear of the original cabinet? If so, I would appreciate seeing what it's supposed to look like. Any idea if the bulb is a significant part of the circuit? Oh, I assume the badge was attached to the front of the cabinet? I would sure like to find one of those badges!!!
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That box or whatever it was is not original. The back panel of you amp looks original. There are 4 jacks. The two closest to the end were the inputs and the two near the center were the speaker outputs. The little cage from the picture I posted on Ampage is over the input jacks. Inside there should be a 68K resistor from each jack soldered together and to a piece of coax that plugs into the preamp via an RCA jack.
Bulb? I don't know what you are talking about.
Those badges are extremely rare. Here's a picture of various different badges.
I think the oldest Sunn O))) badge is the smallest one with the non-bold font.
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OK, that makes sense now, thanks! The cage is there and my confusion was the two jacks on the left were maked, in pen, with an 8 and the two on the right with a 4. They were all connected to the amp output, left 8 ohm tap, rt. 4 ohm tap. Someone was very busy with the insides of this amp back in the day as it is obvious all these mods are very old. Any chance of a picture of the inside of the pre-amp??? Regarding the power bulb, I have read where in some amps they were a part of the circuit. The bulb in this amp is missing.
Thanks again for all the help!
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Hi there,about the power bulb,don't worry about it in this amp.I believe what you are refering to is what used to be done in cheap amps without a power transformer.They series all the heaters on all the tubes to add up to around 117 volts,this may or may not include the pilot light,so if the bulb was missing the amp wouldn't come on.The down side to this is that if the amp won't come on,you have to check all the tubes and the light to see which one is bad.This was real popular in those 5 - 6 tube "table top" radios of the 50's and 60's. As long as you have a power trans.,you're ok.Just replace the bulb,but the amp will work fine without it.Good luck,Mel. P.S. You're lucky,I'd kill to have an old one like that !
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I really appreciate all the info. Not sure what direction I'm going to go to get the amp up and running correctly. Everything that was done is reverseable save for the added jack in the top plate. :x I will probably restore the inputs to their original locations. I'm assuming one output was an 8 ohm and the other a 4? I will keep the forum posted on my progress, that is if anyone is interested. Again, many thanks for all the valuable infromation!!!
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Here are two shots of the inside of the preamp. My amp doesn't have the octal plug to get power from the power amp, it's hard wired. The two output jacks are wired in parallel with leads going to the screw terminals on the power amp. It's wired with #22 white zip cord just like the speakers I had in the early 70's. Note: to get more than one picture per post, click on the blue text that says (more attachments).
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Thanks loudthud, you're the best! Here is a picture of mine. As you can see, the "hack" who worked on it liked to take out caps and not replace them??? What is the voltage rating on the 1000 uf caps and how are the diodes connected, if those are in fact are diodes on top of the caps? There are other issues, YEAH! Maybe they tried to convert this to a PA amp? One input with two or four outputs to mains or monitors? I will probably never know.
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The two caps and two diodes are the voltage doubler circuit to power the heaters of the preamp tubes on 12V DC. On the schematic they are in the upper right hand corner. The 1000uF caps only need to be 10V or more. I see your preamp has twisted wires so the heaters must be running on 6.3V AC. Note that on the schematic, pin 9 of both tubes is grounded and there is no ground at the heater winding center tap, only a cap to ground (check this if you want to restore this circuit).
Switchcraft used to make a little passive mixer with 4 inputs and 4 volume controls which may have been what was mounted in the bottom of your amp. There is a story going around that Conrad used one on the first Beach Boy's PA. So maybe ...
There is another story that Elvis Presley used 5 Dynaco MK III's in his PA at one point. Nobody has said this in a long time, and most of the readers here aren't old enough to remember, (Conrad is a notable exception) but vacuum tube PA's sound really good if they are loud enough. And, ya gotta use JBL speakers!
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That is probably why there were 12AT7's in it which are lower voltage, but why would you want to do that? 1000uf caps are pretty big for those days, I was guessing 25 volts or so. One curious thing I just noticed was the dates on the pots. The bass and treble pots are dated JAN/FEB 1966 respectively. The volume pot is dated JUNE 1966? Assuming it is original which it appears to be, isn't mid 66 kind of late for this amp if it was a bass head? I know I can "what if" this thing to death but could this be an early attempt at a PA amp???
Interesting about the Beach Boys and Elvis. Oh, 1958 D130's in my old bassman cab, re-machined for the larger voice coils and re-coned in Northridge, E-140 in a homemade single cab. My garage speakers for stereo are JBL Model 19's and 4301B Broadcast Monitors.
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I'm not sure about the date the switchover to front controls occured. There is a 66 date code on the 1000uF caps in my amp, the serial number is 14xx. ( I won't be able to look at the amp until Monday.) The DC heater supply is what was used in the Dynaco preamp at the time. I think Conrad made some changes to the preamp circuit vs the Dynaco but I've never compared the schematics side by side. Back in the early 70's I made a clone of one of these preamps and I remember having a hard time finding a 750K pot. There is not much difference in ratings between 12AX7's and 12AT7's except for the gain. The heater ratings are the same.
It's hard to speculate why things were done the way they were on your amp. My guess would be that who ever did it didn't have the money or access to parts that we take for granted today.
I have a smiley face 2x15 cabinet (kinda beat up) that has a pair of D130's with consecutive serial numbers. Too bad the speakers are blown. I wish I could find someone I could trust to re-cone them.
This thread has got me thinking about building an all tube PA. The system I had for years was a pair of Altec A7 cabs with D140's, biamped with a 20W per channel tube power amp running the horns.
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Grumpy old Tom at Aural Technologies in Ashland, http://www.auraltek.com/ ,does a great job! He's done work for me and others I know and haven't had any complaints. He is just sometimes kind of grumpy! If they are the older D130's, the hole for the voice coils will have to be enlarged to accept the new ones. Tom will send them to Northridge and they will also be re-magnitized. It will not be cheap however!!!
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OMG! Tom Garson is still around? We played together for a while, in a band called Echo. That was before he dyed his hair green to play with Johnny Green and the Greenmen. I don't think he liked me much.
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I wouldn't feel bad Issac, I don't think Tom likes anybody too much! I found a discrepancy in the Dynaco Mark III schematic and that of the SUNN Model 60 schematic. The SUNN shows a 50 ohm, 5 watt resistor on the 30/20 can cap. The Dynaco shows a 6800 ohm resistor. It's probably not a huge deal but that is about the only deviation I can find between the two and I was wondering if the SUNN schematic is correct?
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I can't say if that particular Sunn schematic is correct, but the early 200S uses a .1uf coupling cap between the PI and the power tubes, and the schematic shows a .25uf, which is what is in the later 200S. There are also voltage differences with the early amp being around 470v B+ and the later one more like 560v B+. So my guess is that there were running changes on everything including your Model 60.
Greg
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Tom did make me famous, though. Well, somewhat famous, on a regional level. Every time I'd do, well, pretty much anything, he'd say, "Fuckin' Isaac" or "Fuckin' Isaac, man." He said it so often that it made its way into the local language. Our singer was visiting a friend in Roseburg. The friend dropped something in the kitchen and said, "Fuckin' Isaac!"
Sally replied, "What did you say?"
"Fuckin' Isaac. Everybody says it. No one knows where it came from."
One thing about Tom is that he was an amazing guitar player. Amazing not because he's good, although he is very good, but because all of his left hand fingertips have been cut off. Just the first joint of the index finger, but the second joint on the others. Combine that with the fact that he's quite short, is it any wonder that we caled him Tom Thumb? And then, when he dyed his hair green, how could we not think of leprechauns?
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Back to the Model 60. I examined my amp against the schematic and there are differences.
The input to the power amp has a resistor to ground marked 1 meg and 470K. Mine is a 40 watt and it has the 470K. A MKIII Dynaco I have also has the 470K.
The schematic shows the first 7025 with a 1K cathode resistor. My preamp has a 2.2K there.
The schematic shows both 7025's with pin 9 grounded. On mine, only the first 7025's pin 9 is grounded.
The schematic shows an extra 10uF cap on the middle B+ node in the preamp. My amp does not have this. It has a 4 section 10uF @ 450V. The incomming B+ has two sections in parallel and one cap per node with 10K decoupling resistors.
The common side of the output transformer is grounded.
FYI the 1000uF caps are rated at 12V.
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Thanks Loudthud, Mine does have the 1K resistor on V1a cathode. Another question, do the Bass/Treble boost make much difference? Mine don't seem to make any difference. Do you have a pic of the inside of the power amp?
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My amp is a 40 watt so it has a Mk IV power amp. I got it on ebay and the power amp broke loose during shipping :x. Thats another story. Anyway, I've never turned that amp on since I got it so I can't comment on the tone controls. They might work better with a 12AX7 since they are in a feedback loop. The MK III power amp I have had some serious mods when I got it so I don't think pictures will be of any use to you. I did notice it looks like your transformers have been re-painted.
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Thanks, I also have the 470k and no 1meg in the power amp. I have to believe the boosts should make a difference so perhaps I'll try replacing them just to see what that does. Thanks again.
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Hi Loudthud,
Is your pre-amp open on the sides? Mine only has a piece of aluminum on the bottom and the sides are open. I have some spst switches coming so I'll check to see if they make a difference. Do you happen to know how to check them to see if they are Bad? Thanks for all the help you've given so far!
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Here's a picture of the cover for my preamp. It's held on with 4 screws. It has holes near the front panel but no screws have ever been installed there.
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Yup, someone must have cut the sides off. Mines just the bottom. I figured Sunn wouldn't have sold it like that. I guess I'll try to find a piece of aluminum and duplicate the cover to look like yours. I'll get this baby back up and running right. Thanks again for your help. It's been invaluable!!
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Just to update,
I was able to do a reasonable job on the pre-amp cover. I also put in a capacitor kit into the Mk III from Triode Electronics. It handles 630 volts and increases capacitance quite a bit. I tried her out and she sounds very clean but when a bass or guitar is plugged in it's got that hum thing strong. Without an instrument in she can go up to ten with just a slight hum and blow like you like to hear. I think next I'll try to improve the input cable to the preamp from the caged input jacks. I used an old white instrument cable and soldered on an RCA pin. If i touch it I hear a bit of hum when I squeeze it a bit so it's probably not quite cricket. Other than that the power section seems as it should and the preamp hopefully needs only an improved cable. I did replace both boost switches. When on the replacements show a low ohms reading and over limit when off. The old ones only read OL. It does change the tone but only slightly.
Loudthud I think you said you used coax cable for the input connect . Is that different from shielded instrument cable?
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Increased capacitance is not a good thing for your GZ34 rectifier tube so moderation should be exercized. If the grounding is not optimal, and it's usually not when a multi-unit can cap is used, you can get a buzzing type hum that's hard to get rid of. How many ground wires go to this cap board? Did you replace the 1000uF caps and the voltage doubler that powers the preamp tubes heaters?
Regular instrument cable should be fine. Some types of coax intended for radio frequencies can be micophonic but any "audio" coax should be ok. Look on the schematic and there is a 10 ohms resistor between the power amp's ground and the ground to the preamp. Check it with an ohm meter to make sure it's still good. There will probably be a short across it when the preamp is plugged in (that's ok).
There is one little problem that may come up. The GZ34 is supposed to delay turn-on for 10 seconds or so. This prevents the 500V B+ from getting to the 450V cap in the preamp. When the amp was made, the caps could stand over voltage for a few seconds but todays caps arent quite as tolerant. If you replace the GZ34 with solid state diodes, it will be something to be dealt with.
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The cap board bolts to two of the transformer bolts. One bolt grounds the entire thing. I'm sticking with tube rectification for the warm-up time. The board uses 50uf for each section so maybe it is too much. I didn't put in the 1000uf's since it seems the 7025's are now paralleled for 6.3 volts. Would you recommend that I return those. and ground pin nine etc.
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I checked the 10 ohm resistor. I had replaced it. I also tried the MkIII through an old Fisher preamp/tuner. It had no hum at all. When I reconnected it the hum was there when an instrument is plugged in. If I touch the strings or either chassis the hum drops to an acceptable level. As far as sound goes the amp sounds nice and tight and clean, definitely impressive for bass.
I also checked the preamp wiring and replaced the wires to the lamp. They crackled when I touched them with a chopstick and the lamp flickered. I also found another wire going from one ground point to another for no apparent reason. Sadly removing it didn't change things as far as the hum.
I think I'll try to replace the input cable to the preamp and see if that makes a difference. When the input is unplugged from the preamp I can turn the volume right up to max with minimal hum. All I can say at this point is hummmmm.
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Doh!!! (A Homer Simpson moment) The amp has no ground switch or death cap. Install a grounded power cord and the hum should go away.
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Real double dah. Sometimes I just out think myself. Something about seeing the amp from the trees...Thanks for telling me what should have been obvious. I'll report back on the results.
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That did the trick...Hearing it now I can see why this Sunn Bass amp was a must have when they began and why they became so popular with all the bands at the time. WOW! Now I need to find a folded horn cab to go with it. That and I think I'll try to make a replica plate for the amp grille... Thanks again Loudthud for your help and patience.
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I am a complete know-nothing boob when it comes to the workings of electronics. I haven't understood hardly a F...ing thing you guys have been talking about. Yet, I find myself checking up on this thread every day. It's somehow fascinating even though I haven't a clue what you're talking about. How is that possible ? LOL
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I guess it's seeing if this thing can actually get back to working as it should. Plus it's interesting to see what possible issues amps have. They're all basically the same and if you're not careful you start trying to experiment yourself. Then it's amp hell time for sure. It's a good kind of hell though in its own way. Ultimately I love the whole idea that you can work on them to restore them versus modern stuff which is so disposable and not really meant to last.