Kay Reverb Model 710

[RadioComm]

Hope everyone having a great week-end.

Just finished cleaning/reorganizing my basement after 30 years of hoarding. In my archeological digs  , I found a degutted Kay Reverb Model 710 Unit that a good friend of mine donated to me over 20 years ago. Don't know the story behind it. This is going to be my next project. Found the schematic on the SurfGuitar101 forum, and it had been provided by tubeswell (Thanks tubeswell).

Currently I'm in the preparation phase by putting a BOM together and using  DIYLC for the layout. I have the following questions:

* Haven't measure the PT yet, but if it is bad, what voltage should I be looking for?
* For diode D1, what is a TH-50?
* Can anyone read the value for C6? Looks like .05 µF / 100v. Does that sound reasonable?

Thanks again

ttfn

[Williamblake]

Wow, nobody is home. Hope the old germanium diodes found a nice new job but getting something similar might be hard.

[RadioComm]

Wow, nobody is home.

Complete empty nester. Just a PT, one transistor, and a resistor decided to stay. Never asked my buddy what the back story was. He came over one day to play guitar, and I guess he must have been cleaning out his basement and brought over a box of goodies. Like me, he used to take hand-me-down projects too, so he may not even know (or remember...)

Hope the old germanium diodes found a nice new job but getting something similar might be hard.

I found germanium diodes at tubes and more and amazon, but they all have the 1Nxx designation. Nothing on a "TH-50". So still not sure which one to go with... Looked in the attached Sylvania's germanium diode handbook, but still all designators are 1Nxx. Still researching...

Thanks.

ttfn.

[sluckey]

I found germanium diodes at tubes and more and amazon, but they all have the 1Nxx designation. Nothing on a "TH-50".

That diode is just being used as a low voltage rectifier and is most likely a silicon diode. Any of the 1N400x series will work. I would use a 1N4007 or a 1N5408 just because I have plenty on hand.

[RadioComm]

I found germanium diodes at tubes and more and amazon, but they all have the 1Nxx designation. Nothing on a "TH-50".

That diode is just being used as a low voltage rectifier and is most likely a silicon diode. Any of the 1N400x series will work. I would use a 1N4007 or a 1N5408 just because I have plenty on hand.

Understood. Thanks sluckey. Ditto, I have plenty 1N4007's in my stash.

ttfn.

[RadioComm]

* Haven't measure the PT yet, but if it is bad, what voltage should I be looking for?
* Can anyone read the value for C6? Looks like .05 µF / 100v. Does that sound reasonable?

Just measured the PT. It's outputting 15.9 VAC. Considering the specs for the transistors, I think the PT voltage is OK. So running with it.
Also, until I hear otherwise, I'll also run with a .05 µF / 100v for C6.

Thanks

ttfn

[Williamblake]

Maybe the reverb driving circuit wasn't built to last anyways? Find something to copy to put in the cabinet. Dont feel obliged and dont scratch the cabinet.

[RadioComm]

Maybe the reverb driving circuit wasn't built to last anyways? Find something to copy to put in the cabinet. Dont feel obliged and dont scratch the cabinet.

You're absolutely right! Started the diylc layout, but when searching for a 2n2613 transistor there was absolutely nothing out there. The price for the 2n408 were ridiculous. This said... It's fun doing the layout. This project is definitely for fun and I'm  not trying to be trying cost effective. But at the same time, I'm *definitely* considering other options using the existing parts.

Thanks

ttfn

[RadioComm]

Huzzah! Tubes & More just received new transistors. Including the ones I need (2n2613/2n408). Ordering them now.

Did look into the following two alternative circuits:

http://www.generalguitargadgets.com/effects-projects/reverb/stage-center-reverb
https://sound-au.com/project34.htm

But decided to continue with the restoration. No reason...  Just because...

ttfn

[RadioComm]

Finished the layout...

Update: Actually, I don't think I'm finished. Did some quick tracing this morning, and there's still (I think  ) some issues. I'd rather trace a couple more times before someone spends precious time reviewing the layout. I need more time, and I'll update this post soon. Thanks.

I'm not very good or confident at layouts. I know this is a huge ask, but could someone please check & correct the layout. That would be such a big help 

I'm attaching:
    * The schematic
    * A png of the layout
    * A diylc layout file

Thanks so much.

[RadioComm]

Did some more tracing, and indeed there was a problem area. So let me try this again:

Finished the layout...
I'm not very good or confident at layouts. I know this is a huge ask, but could someone please check & correct the layout. That would be such a big help 

I'm attaching:
    * An annotated schematic labeling the transistors
    * A png of the layout
    * A diylc layout file

Thanks so much.

[RadioComm]

No takers. It was a big ask. I've checked out the layout a couple more times, and I think I'm mostly there. So I'm getting starting, and I'll check off the connections on the schematic and layout as I solder them. And just go from there. I did make a couple of changes to the layout: (Twilight zone... Incomplete post. The complete two part post further down...)

[sluckey]

Man, you must be hard up for a project!   

[RadioComm]

No takers. It was a big ask. I've checked out the layout a couple more times, and I think I'm mostly there. So I'm getting starting, and I'll check off the connections on the schematic and layout as I solder them. And just go from there. I did make a couple of changes to the layout:

* Corrected the direction of the diode
* Couldn't find C8 500uf 25V, so will be hooking up two 250uf 25v in parallel. So hooking up ground to opposite terminal strip
* Moved the VAC wires from the terminal strip to the on/off potentiometer. The lugs on that terminal strip are just too close to the footswitch jack. I'm going to route those vac wires as far away as possible from everything else.

Replaced the terminal strips. The originals had lugs with absolutely no holes in them and the wires wrapped around two or three times.

I've posted a couple pics for the starting point of this project, plus the updated layout. I've also posted a picture of the internal circuitry for a refurbished stock Kay m710. That "TH-50" diode is certainly a weird one... I've never seen one that shape. I'm guessing the "M" on top is for Motorola... Does anyone know more about this diode format? (only one attachment made it through on this post... Added them further down)

Thanks.

ttfn

[RadioComm]

Man, you must be hard up for a project!   

Lol  Yeah, it happens... 

[Williamblake]

Cmon, where just humans.

[RadioComm]

Things are posting weird... Here are the additional attachments...

[sluckey]

Diodes come in a bajillion shapes and sizes. It's all good as long as the leads are properly marked.

[RadioComm]

Finished the wiring. Only changes to layout was :
* Swapped leads for real estate purposes
* Added missing connection.

So dry signal comes through. But not reverb signal. Trouble shooting:
* The two reverb tanks my friend gave me exhibited the same issue with the Kay as with my stock super reverb. No reverb signal coming though, but when I hit the springs you will hear them.
* Checked the reverb cables
* Plug in my champ reverb tank into the kay and it works. But with increasing distortion as I raise reverb level

So in the market for a reverb tank, but not sure what impedance to get:
* As seen in the first post picture, stock tank has numbers "2802" and  "6314", but doesn't seem to match accutronics numbering scheme.
* Don't know the history of the accutronics tank that my friend gave me... So not sure whether it's a compatible impedance.

So how can I determine which tank to buy? Can a reverb tank be fixed?

Thanks so much.

ttfn

[RadioComm]

Visually inspected the Kay reverb tank, and the input wires were soldered to the transducers, but the input transducer itself was loose. So looked no further.

The Accutronics tank has pinch connectors, so reseeded the input connector, and things worked and sounded good. So once again, I'm going to pick my ears over numbers, and just ignore impedance and order a new Accutronics tank to match the old one.

Also ordered male rca to bare wire cables. Because of the clearance between the cabinet and the tank, Kay routed their wires through the rivet holes of the rca tank connectors and soldered them on to the rca connector leads on the inside. Must have been a pain to service these, since the reverb tank cables were soldered on both ends. Soldered into the circuit and soldered into the tank.

This project was fun. It's the first time I've converted a schematic to a layout.

Take care everyone.

ttfn.

[Willabe]

......No reverb signal coming though, but when I hit the springs you will hear them.

That means the verb recovery is working.

So either the verb input driver stage or the tanks input is not working.

Glad you got it fixed.   

[RadioComm]

Turns out that something is wrong...

When playing with the guitar, there is a decrease in the signal with some distortion. This degraded audio signal is present in both the dry and the reverb path as set by the footswitch. Since they are identical, I started the troubleshooting in the dry signal path. Followed up by the wet signal path. This was done comparing the schematic with both the layout and the actual implementation, I have not found any issues. I have looked at:
* Circuit paths
* Electrolytic polarities
* Transistor orientation
* Voltage on the OT secondary is 15.85 VAC
* Voltage post rectifier on collector of Q1-2 (2N408 rated at 20 VDC) is 19.45 VDC

Also of note, when plugging in a audio signal generator (@ 100mv) and using an osilloscope:
* The sine wave of the output jack tip has greater amplitude that the input jack tip
* Q1-2 quickly starts overheating

I'm not too sure where to go from here. Any help with direction would greatly be appreciated.

Thanks so much

[sluckey]

I don't see how Q1-2 is biased???

[RadioComm]

I don't see how Q1-2 is biased???

Sorry... Above my pay grade... Is this an observation from the schematic? Thanks.

[sluckey]

The base has no path for dc current to flow, except to emitter or collector.

[RadioComm]

The base has no path for dc current to flow, except to emitter or collector.

Sorry again... Still above my pay grade... But if this observation is from the schematic, I've attached the SS reverberation section from Jack Darr's First Edition from August 1965. He doesn't mention the Kay 710 by name but the schematic looks identical.

[sluckey]

Yep. Looks the same to me.

[RadioComm]

Hello,

Resolved the previous signal issues. Signal level is now good with no distortion. This is what was done:
* Inspected stock images, and noticed that the input driver (Q1-2) was in the "clip".
* Realized that the input driver was intended to overheat, and the "clip" is actually a heat sink. (duh, jumps out and bites me now)
* Figured the input driver was damaged due to overheating, so replaced transistor with a new one.
* Built a heat sink comprised of 18 gauge pure copper sheet metal and a TO-5 heat sink (picture attached). Used thermal paste for coupling. The copper heat sink was fashioned using W1CER instructions (attached).

One last question, I'd like to get a reverb tank with the same specs as the original. Is there a way, and how can I measure the impedance of the tank's input/output. Tried to find specs using the codes on the stock tank (pictured 2802 - 6314), but am not able to find any.

Thanks.

[Williamblake]

Cool, this seems to turn out so well, impedance corresponding to DC voltage is givven on this page.

https://www.amplifiedparts.com/tech-articles/spring-reverb-tanks-explained-and-compared

[RadioComm]

Indeed a great article. I usually access it thought their tubes and more site:
https://www.tubesandmore.com/tech-articles/spring-reverb-tanks-explained-and-compared

What I was missing from this article, is that I didn't understand what the resistance was on the row below the "input impedance (@ 1kHz)". But surfing the internet, I found the following article:
https://studiosoundelectronics.com/reverbdcchart.htm

Which has that row marked.  Now I get it. It's dc resistance. And I know how to measure that. And now I can use that measurement to ballpark the impedance.

So I measured the Kay's reverb tank, but since the input is busted, I wasn't able to get a reading on the input. The output measures 170 Ω DC resistance. This is confirmed by another thread referencing a similar issue with a Kay 710 reverb tank:

"Just talked to my tech (who was driving at the time and couldn't give me the codes stamped on the pan, but could tell me the in and out impedances were both around 170 Ohms..."

So these are the specs that I'm going for:
* Input 1,475 impedance (close enough to 170)
* Output 2250 impedance (close enough to 170)
* Insulated input/Grounded output (from stock pictures and solder stubs from the original tank. Wires were clipped instead of de-soldered)

This matches the following reverb tank:
https://www.tubesandmore.com/products/reverb-tank-mod-4fb3a1b-long-decay-2-spring

The above unit has both input/output grounded, so I'll have to disconnect the input from ground.

I'll be ordering it soon.

Thanks everyone for the responses. 

Take care.

[sluckey]

Indeed a great article. I usually access it thought their tubes and more site:

Here's the same info in pdf format in case you want to save it to your device...

[RadioComm]

Received the tank. Did the following
* Isolated the input connector from the tank casing following the instructions in this link: https://bmamps.com/v01/wp-content/uploads/2017/10/How-to-Reverb-Tanks.pdf
* Not enough clearance between the tank and the chassis to accommodate either the RCA jacks or the power cord retainer. So soldered the RCA cables directly to the jacks (interior chassis as pictured), and whittled away at the retainer. It all fits now.

Tone wise the signal is now transparent, but there is still the following issue:

There is a *definite* increase in volume when the guitar plays through the reverb than when it is directly hooked up to the amp. This boost stays the same irregardless of the amount of reverb used.

Any insights?

Thanks so much.

[sluckey]

There is a *definite* increase in volume when the guitar plays through the reverb than when it is directly hooked up to the amp. This boost stays the same irregardless of the amount of reverb used.

Is this really a problem? If so, increase the value of R8. Experiment until satisfied.

[RadioComm]

There is a *definite* increase in volume when the guitar plays through the reverb than when it is directly hooked up to the amp. This boost stays the same irregardless of the amount of reverb used.

Is this really a problem? If so, increase the value of R8. Experiment until satisfied.

Problem? Maybe?  The increase in volume is really significant, and I'm getting some noise. This is the same type of noise I would get If cranked my amp up all the way to 11. Checked for grounding issues, but couldn't find any.

Sorry, maybe I should have mentioned this in the previous post... Is R8 still a viable candidate? I'm guessing you're referencing the R8 on the output jack. I was thinking a resistor closer to the input jack somewhere in the drive stage. Also by how much should I increase the resistance.

Once again, thanks so much sluckey for your help. 

[sluckey]

R8 will only affect the level of the dry signal. The reverb signal remains unaffected.

I would try 330K, 470K, etc. Probably easier and faster to just replace R8 with a 1M pot and adjust until you are satisfied with the output level. Then measure the pot and replace with the correct fixed resistor.

[RadioComm]

I would try 330K, 470K, etc. Probably easier and faster to just replace R8 with a 1M pot and adjust until you are satisfied with the output level. Then measure the pot and replace with the correct fixed resistor.

Will do. Since dry signal, I will be experimenting with the R8 hooked up to C7.

R8 will only affect the level of the dry signal. The reverb signal remains unaffected.

Does this mean that when I increase the amount of reverb, there will be an increase in volume?

Thanks again for the help sluckey.

[RadioComm]

All done. This time for real.

Thanks again sluckey. Using an empty post, I added a 33K resistor in series to R8 of the dry signal path. There is a slight increase in volume when increasing the reverb signal, but not an issue at all. Most of the time I don't use a whole lot of reverb, and for my sweet spot this is just perfect.

Also the noise issue that I was having was AC interference. When looking at the stock picture of the layout, one can notice that all the transistors are completely on the opposite side of the PT. Unfortunately I did not take this into account when doing my layout. Next time I do a layout, I most definitely will. As seen in the attached pictures, I solved the problem by wrapping the AC wires with solderable copper tape that I grounded. The noise levels are perfectly acceptable now.

Hope everyone has a most wonderful Winter/Holiday season, and for those who celebrate Christmas, Merry Christmas.

ttfn

[vandoog]

Hey there! absolutely love this thread. I picked one of these up and its been super helpful! Mine was not passing any guitar signal other than reverb pan noise until a recap.

I'm having an issue now where the reverb doesn't effect the guitar signal UNLESS I run a jumper from the isolated sleeve of the input on the pan to the grounded sleeve of the output

Any thoughts on this? The schematic you posted does show the pan input grounded if I am reading it right but stock there was no ground wire leading to the pan nor to see one in photos or your build. I do notice in your layout you add one. Ty for the help!

[RadioComm]

Hey there! absolutely love this thread. I picked one of these up and its been super helpful! Mine was not passing any guitar signal other than reverb pan noise until a recap.

I'm having an issue now where the reverb doesn't effect the guitar signal UNLESS I run a jumper from the isolated sleeve of the input on the pan to the grounded sleeve of the output

Any thoughts on this? The schematic you posted does show the pan input grounded if I am reading it right but stock there was no ground wire leading to the pan nor to see one in photos or your build. I do notice in your layout you add one. Ty for the help!

Been *real* busy lately... Have to put the fun stuff on the back burner...

1) As you noticed, the original has the reverb input isolated and the output grounded. When stripping the 710, the previous owner had cut the wires on the reverb tank. And since Kay soldered the wire directly to tank, it was apparent that the reverb input was isolated, and the output grounded.

2) Sorry. The layout and the pictures are misleading. Indeed I grounded the reverb RCA jacks on the chassis, and the cables in turn are soldered to those jacks. But as stated in reply #31:

* Isolated the input connector from the tank casing following the instructions in this link: https://bmamps.com/v01/wp-content/uploads/2017/10/How-to-Reverb-Tanks.pdf

So my unit has the reverb input isolated, and the output grounded.

3) When toying around with grounding the reverb tank, the *only* case where no sound was making it through was when nothing was grounded. So maybe a bad solder joint where the reverb output is grounded... Maybe? Can't really think of anything else.

Take care. ttfn.

[vandoog]

thanks for the reply @RadioComm

Oddly it the output must have a secure ground since the I've gotten it to work by soldering a piece of solidcore wire inside the tank from the ground lug of the input to the ground of the output. strange stuff, honestly confused

It does sound great but the reverb signal is definitely distorted! Its not a bad sound but I wonder if this has to do with the higher wall voltages we have nowadays compared to when this thing was made? any thought on how to tackle that are appreciated

worst case scenario I'll probably slap a 3 prong chord on it so I don't get the polarity mixed up with my champ and call it done! kind of a unique sound on its own with the subtle bit of distortion it throws in

[RadioComm]

With this project, the only time I experienced slight "distortion" in the reverb signal was when trying different reverb tanks that I had hanging around. Once I purchased a properly matched tank, the "distortion" went away. Obviously you are using the stock tank, but maybe an impedance mismatch...

Take care everyone.