Sunn Dymos reverb and speakers

[hadyourphil]

I have a Dymos brought to me for repair. When I turn up the reverb control, I get a noticeable change in eq of the audio being passed through, but no noticeable reverb effect. The spring assembly seems to be good. What should I expect, performance-wise, from the reverb? And, if that's not enough, one of the speakers has a detached voice coil wire with no repair possible. Does the Dymos use JBL speakers and what would be a good replacement?

[EdBass]

That's a rare bird; since I've never seen one in person I can't help you with what the reverb should sound like, but it seems that in 1969 the Dymos was available with Sunn Transducer speakers only but in 1970 a JBL D123F upgrade was available. Most of the Sunn reverbs I'm familiar with from that era are pretty lush; kind of "Fenderesque" if that helps.
I think the '69 had the Orion's vertically striped grill (sort of like an asymmetrical "ultra hip" version of the Kasino grills of the era), and the '70 model used the standard rectangular pattern Sunn grill cloth.

If the one you have has JBL's it should visibly be pretty obvious, they are pretty distinctive looking.
There are probably as many good replacements as there are opinions as far as the standard Sunn drivers go, but if it's the old AlNiCo JBL's in the amp it will be difficult to find a current driver that can actually cop that vibe.
IMO of course!

[hadyourphil]

As you can see, it has Sunn stickers on the speakers, but does that indicate Sunn made them? And, it definitely needs TLC! I cleaned the controls on it and fired it up. It sounds pretty good, but definitely needs a speaker, or two that match. I found a schematic on the 'net. I'll pull the amp out and see what's weird around the reverb circuit.

Regarding the speakers... I guess I could get the one with the broken voice coil wire reconed, but it has a treated paper surround and what appears to be a metal dome. Don't want to have dissimilar speakers, definitely. In researching the JBL speakers, they would be D123F's. I also found reference to a repair kit called C8R2125, but don't know where that would be avaliable.

[george]

So what year did Sunn switch from the "mod" stripped grille cloth? I have a Dymos chassis in the queue for repair and it may turn into a restoration requiring a new enclosure. Plans would be nice but I won't hold out hope that someone has them.

[EdBass]

As you can see, it has Sunn stickers on the speakers, but does that indicate Sunn made them? And, it definitely needs TLC! I cleaned the controls on it and fired it up. It sounds pretty good, but definitely needs a speaker, or two that match. I found a schematic on the 'net. I'll pull the amp out and see what's weird around the reverb circuit.

Regarding the speakers... I guess I could get the one with the broken voice coil wire reconed, but it has a treated paper surround and what appears to be a metal dome. Don't want to have dissimilar speakers, definitely. In researching the JBL speakers, they would be D123F's. I also found reference to a repair kit called C8R2125, but don't know where that would be avaliable.

Those are AlNiCo "Sunn Transducer" speakers, the label is correct. I think they were made by CTS.
The JBL’s are a much different driver, waaaay more substantial.

Heavy cast frame, huge AlNiCo motor by comparison. You can find the old Sunn Transducers on eBay from time to time, they are very inexpensive compared to the JBL’s.

So what year did Sunn switch from the "mod" stripped grille cloth? I have a Dymos chassis in the queue for repair and it may turn into a restoration requiring a new enclosure. Plans would be nice but I won't hold out hope that someone has them.

I THINK the striped grill was only in 1969, but I’m no expert on transistor Sunns.

[hadyourphil]

Now I'm really stumped! I pulled the amp out to try to determine what's wrong with the reverb. Spring and transducers are fine. However, the voltages I have are very different from what's on the schematic.  On the red wire (primary) of T-2, the schematic calls for 10v. I have 22v. And the power supply's +/- 15?? volts read +/- 5.2v. The schematic I am using was found on the internet and seems to correspond with the amp otherwise. Anyone have any suggestions/comments??

[hadyourphil]

Un-stumped, at least as far as the reverb goes. Turns out the 1/4" input jacks were corroded enough to affect input level to the point that the reverb would not work. An accidental discovery. Guess the voltage discrepancies are OK as long as the thing works.

No one heard of the speaker repair kit referenced above?

[EdBass]

Congrats on the easy fix for the reverb!
The C8R2125 is a factory recone kit for the JBL D123, which is a moot point in your scenario for a couple of reasons.
First, I think they are most likely unavailable.
Second, those speakers in the Dymos pictured aren't JBL's, and unless you have another set of speakers not pictured in your posts, even if you do find the C8R2125 kits, the JBL kit won't have any use except for the adhesive and maybe the gasket.

[hadyourphil]

Good point on the speakers. And, I'm not so sure about the reverb fix. It doesn't sound as good today. A real head scratcher.

[hadyourphil]

I re-engineered the reverb with great results! If you look at the piece of schematic I posted earlier, you will note that T-2, the transformer that drives the reverb, has one leg of the secondary grounded. And, the reverb has one leg of both transformers grounded. This looked like too much coupling to me, so I lifted the ground connection on both the reverb input transformer and T-2's secondary and connected them together, effectively isolating them more from the reverb output. Voila! Reverb that doesn't get midrangey and actually has some "twang"! By the way, there is a big difference in the input and output impedances of the Sunn Gibbs reverb unit. The input measures 1.2 ohms (appx) and the output measures 172 ohms (appx). This is unlike the common Hammond organ reverb springs that measure about 168 ohms both on the input and output transformers. The Hammond spring, though, does isolate the input transformer in the same fashion that I have now isolated the Sunn spring. And, with a steady hand and a bit of profanity, I was able to repair the broken speaker! All in all, a productive night.