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Kay 515 Tube Amp...or is it?
Old 15th July 2020
  #1
Gear Nut
 

Kay 515 Tube Amp...or is it?

I just picked up this amp.  It will be my first Kay amp.  Usually the Kay tube amps I see are widow maker amps that I pass on.  So when I saw the transformers and the description of the tube line up, I made an offer.  It was described as 515.  It does have a 15" speaker, but when I searched the 515, it's not quite the same.  I found the exact amp on ebay but no model given.  Only described as rare tremolux circuit. There are reminiscence of a schematic and parts list on the bottom.  When I begin cleaning I'll see what I can find.  Here are pics.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-p1290285.jpg   Kay 515 Tube Amp...or is it?-p1290286.jpg   Kay 515 Tube Amp...or is it?-p1290287.jpg   Kay 515 Tube Amp...or is it?-p1290289.jpg   Kay 515 Tube Amp...or is it?-p1290290.jpg  

Kay 515 Tube Amp...or is it?-p1290293.jpg   Kay 515 Tube Amp...or is it?-p1290294.jpg  
Old 15th July 2020
  #2
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enorbet2's Avatar
I can't recall if the Model 515 is shown and I don't have any of my copies handy to check but I do recall that Jack Darr's "Electric Guitar Amp Repair Handbook" had numerous Kay tube and SS amp schematics. I did find in a cursory search a free transcript online but it only includes the main section and not the voluminous Appendix with hundreds of scheatics of old gear. The Index is divided into several sections based on power output so I couldn't affirm the 515 is one of them but it's a decent place to start looking.

It's out of print but still available on many used books sites for cheap.
Old 15th July 2020
  #3
That amp reminds me a lot of my bass player's amp back in college in the '60s, except that his didn't have tremolo.

As bass amps go, it was pretty horrible.
Old 16th July 2020
  #4
Gear Nut
 

Quote:
Originally Posted by John Eppstein View Post
That amp reminds me a lot of my bass player's amp back in college in the '60s, except that his didn't have tremolo.

As bass amps go, it was pretty horrible.
The posting for this amp described it as a bass amp. The faceplate is badly rusted, but the one on ebay shows 4 inputs labeled as instrument. Hopefully it sounds descent for guitar. I've had luck with a 1x15 guitar amp. It's the 6" speaker amps I worry about.
Old 16th July 2020
  #5
Gear Nut
 

Quam 15" speaker looks like 1961. One small tear in the cone
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200715_215317.jpg   Kay 515 Tube Amp...or is it?-20200715_220006.jpg   Kay 515 Tube Amp...or is it?-20200715_220012.jpg  
Old 16th July 2020
  #6
Gear Nut
 

Chassis pics.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200715_221216.jpg   Kay 515 Tube Amp...or is it?-20200715_221320.jpg   Kay 515 Tube Amp...or is it?-20200715_221351.jpg   Kay 515 Tube Amp...or is it?-20200715_221402.jpg  
Old 16th July 2020
  #7
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enorbet2's Avatar
Quote:
Originally Posted by tigerzilly View Post
The posting for this amp described it as a bass amp. The faceplate is badly rusted, but the one on ebay shows 4 inputs labeled as instrument. Hopefully it sounds descent for guitar. I've had luck with a 1x15 guitar amp. It's the 6" speaker amps I worry about.
If it has Tremolo, and it looks like it does, it's unlikely it was billed as a Bass Amp. It is my guess it should make a decent guitar amp. Those look like very substantial transformers for 2 x 6V6s. If you don't like how it sounds it doesn't look too demanding to essentially turn it into a Deluxe like this
Old 16th July 2020
  #8
Gear Nut
 

Here's the schematic.
Attached Files
File Type: pdf Kay_515.pdf (447.0 KB, 9 views)
Old 16th July 2020
  #9
Gear Nut
 

Looky here. You can actually read a lot of this. It doesnt say 515 but schematic should match up. It does refer to it as a guitar amplifier. Nor sure why I see it refered to as a bass amp by some.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200716_102904.jpg   Kay 515 Tube Amp...or is it?-20200716_102849.jpg   Kay 515 Tube Amp...or is it?-20200716_102830.jpg  
Old 16th July 2020
  #10
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davet's Avatar
 

My First Amp

My first amp was a Kay and I still have the POS guitar that came with it. I think the amp was OK, small, but I could walk to band practice with it. The guitar on the other hand was awful. I'm amazed to this day I actually learned to play on it.
Old 16th July 2020
  #11
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enorbet2's Avatar
Quote:
Originally Posted by tigerzilly View Post
Here's the schematic.
Well the design does have some rather silly points like the fact that the Volume and Tone controls effectively duplicate what's on most guitars because they precede the Input to the first stage of amplification but I'd still like to hear how it sounds because Simple is most often really Good.

That said, I'd probably do considerable mods if I intended to use the amp. Obviously removing the "Death Cap" and subbing in a 3-wire power input would be first on the list, but some of those power cap values are half of what was common even on Tweed Fender amps. I'd upgrade the power caps fo sho.

As I suspected from the tube complement it would be pretty easy to convert the preamp (and possibly the driver stage) into something akin to the Deluxe I listed, but at the very least since it really was never very useful to run more than one instrument at a time into any instrument amp, I'd remove the secondary input system, place the two 12AX7 preamp stages in Series instead of Parallel so I could place Volume and Tone between the two stages, greatly expanding gain staging control. I would also create some isolation for each side of the Output stage by adding resistors to each 6V6 pins 4 and 5

I am quite curious about those fairly massive transformers, now more than before considering the output is not only just 2 x 6V6s but cathode biased! It's doubtful it puts out much more than 10-12 Watts so why such Big Iron? It is particularly interesting to me because they could mean the amp has the fundamentals for an excellent upgrade. Kay may well have used the same transformers for many different amps, including those of higher power employing other power tubes. Interesting!
Old 17th July 2020
  #12
Gear Nut
 

I didn't expect replacing the grill cloth to be such a big deal. The speaker baffle isnt made for removal. It takes a bit of cabinet surgery.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200716_101219.jpg   Kay 515 Tube Amp...or is it?-20200716_102309.jpg   Kay 515 Tube Amp...or is it?-20200716_140756.jpg   Kay 515 Tube Amp...or is it?-20200716_145952.jpg   Kay 515 Tube Amp...or is it?-20200716_212631.jpg  

Kay 515 Tube Amp...or is it?-20200716_212634.jpg   Kay 515 Tube Amp...or is it?-20200716_150409.jpg  
Old 17th July 2020
  #13
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enorbet2's Avatar
Very nice work, tigerzilly, and now I can see part of the reason why. You have a nice selection of tools with an eye toward balance between Hi and Lo Tech... the right tool for the right job and the knowledge that both implies and engenders. Congrats!
Old 19th July 2020
  #14
Very nice job. I hope the amp is worth the work!
Old 19th July 2020
  #15
Gear Nut
 

The right tool and some luck! It seems to be a nice sturdy cabinet.
Old 19th July 2020
  #16
Gear Nut
 

Quote:
Originally Posted by John Eppstein View Post
Very nice job. I hope the amp is worth the work!
Thanks! Perhaps thats my problem. I do it for the fun of it. Not sure it will be worth much. Ive have yet to refurbish an old tube guitar amp and not be happy.
Old 20th July 2020
  #17
Quote:
Originally Posted by tigerzilly View Post
Thanks! Perhaps thats my problem. I do it for the fun of it. Not sure it will be worth much. Ive have yet to refurbish an old tube guitar amp and not be happy.
Well, you sure as hell do a good job!
Old 5th August 2020
  #18
Gear Nut
 

Quote:
Originally Posted by enorbet2 View Post

I am quite curious about those fairly massive transformers, now more than before considering the output is not only just 2 x 6V6s but cathode biased! It's doubtful it puts out much more than 10-12 Watts so why such Big Iron? It is particularly interesting to me because they could mean the amp has the fundamentals for an excellent upgrade. Kay may well have used the same transformers for many different amps, including those of higher power employing other power tubes. Interesting!


I'm really bumming out now. I just did a recap of the amp and replaced the power cord. Was seeing signal passing at 55 volts. When I dialed up the voltage to 118, I heard a subtle pop and my power supply breaker tripped. No burnt smell. Reset the power supply breaker and dialed up the power to 60 volts and now have no signal passing. At 60v, I measured about 120 volts at the rectifier plates. My B+ was about 12v.

I plugged it into a light bulb limiter. Pulled all the secondary wires from the transformer. Still getting a bright light. Looks like my power transformer just went on me.
Old 5th August 2020
  #19
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enorbet2's Avatar
It's been 50 years since I used a light bulb as a limiter so I'm not 100% certyain I'm following your troubleshooting path but before I'd assume the PT is bad, I'd surely check that rectifier tube. Pare down. Isolate. Test and measure everything, right?
Old 6th August 2020
  #20
At 55 volts was the light bulb shining at all brightly?

If so, you have a short somewhere.

Are you certain you didn't install a cap backwards?
Old 7th August 2020
  #21
Gear Nut
 

Quote:
Originally Posted by John Eppstein View Post
At 55 volts was the light bulb shining at all brightly?

If so, you have a short somewhere.

Are you certain you didn't install a cap backwards?
I used the light bulb limiter at 118V. Started disconnecting secondaries from the PT to isolate the short but with all the secondaries off the light was bright and the PT is very hot.

I measured secondary voltages off the PT and get 6.6v filament, 600v plate to plate, and 5v filaments. I would start to reconnect the PT if it weren't so hot with subtle smell. Seems to be drawing about an amp with nothing connected.
Old 7th August 2020
  #22
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enorbet2's Avatar
Quote:
Originally Posted by tigerzilly View Post
Seems to be drawing about an amp with nothing connected.
There ya go. Even 0.1 A would be rare on a working PT with absolutely nothing on the secondaries. Sorry, Bro. It probably would be wise to double check those filter cap polarities and solder joints before you sub in a new one.... just to be certain. You know... "measure twice, cut once".
Old 9th August 2020
  #23
Quote:
Originally Posted by tigerzilly View Post
I used the light bulb limiter at 118V. Started disconnecting secondaries from the PT to isolate the short but with all the secondaries off the light was bright and the PT is very hot.
HUH?

If you used the light bulb limiter at 118VAC it didn't do much - that's not how you use one.

You use a light bulb limiter with a Variac. You bring the voltage up slowly. If the bulb starts shining brightly before the voltage is over, say, half way you have a short somewhere.

Quote:
I measured secondary voltages off the PT and get 6.6v filament, 600v plate to plate, and 5v filaments. I would start to reconnect the PT if it weren't so hot with subtle smell. Seems to be drawing about an amp with nothing connected.
You have a shorted PT. Ouch.
Old 4 weeks ago
  #24
Gear Nut
 

Got a new PT installed. ClassicTone 40-18060. It powers up and passes signal. Sounds loud and big with a nice breakup. But....getting a crackly noise coming through. Trem isnt working. Volume goes from nothing to full by 3. I guess i hear more breakup beyond 3, but not more volume. I did some tube swapping. No luck. Its still needs sorting out.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200826_223711.jpg   Kay 515 Tube Amp...or is it?-20200826_223717.jpg   Kay 515 Tube Amp...or is it?-20200826_223728_hdr.jpg  
Old 4 weeks ago
  #25
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enorbet2's Avatar
Heya ...look here for wide-ranging instrument finishing products

https://www.shellac.net/stringed_Ins..._finishes.html

and especially here for photos of available dye colors at full strength. They can be depth and intensity reduced with "thinners"

https://www.shellac.net/mohawk-ultra...-moreinfo.html

EDIT: Hmmm wrong thread?

Last edited by enorbet2; 4 weeks ago at 04:32 PM..
Old 4 weeks ago
  #26
Gear Nut
 

Replaced a handful or resistors. Rewired a cap in the trem circuit. Crackling noise is gone. Trem is working. Volume pots still seem like all or nothing but can be dialed in with the guitar volume. I reassembled the amp. It has a nice tone with good breakup. I still need to make a a back panel.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200827_233515.jpg   Kay 515 Tube Amp...or is it?-20200827_233540.jpg  
Old 4 weeks ago
  #27
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enorbet2's Avatar
Quote:
Originally Posted by tigerzilly View Post
Replaced a handful or resistors. Rewired a cap in the trem circuit. Crackling noise is gone. Trem is working. Volume pots still seem like all or nothing but can be dialed in with the guitar volume. I reassembled the amp. It has a nice tone with good breakup. I still need to make a a back panel.
If your amp is actually true to the schematic you provided it's pretty easy to see why the Volume controls are "hinky". Note that the top lug is unused. This means Volume is not being employed as a Potentiometer but as a Variable Resistor. Audio Taper has little meaning so early in the circuit used as a mere resistance to ground instead of a potential. Once it crosses the threshold... Bam! Full On.
Old 4 weeks ago
  #28
Gear Nut
 

Quote:
Originally Posted by enorbet2 View Post
If your amp is actually true to the schematic you provided it's pretty easy to see why the Volume controls are "hinky". Note that the top lug is unused. This means Volume is not being employed as a Potentiometer but as a Variable Resistor. Audio Taper has little meaning so early in the circuit used as a mere resistance to ground instead of a potential. Once it crosses the threshold... Bam! Full On.

Any suggestions to improve. I also notice the trem doesnt have the depth I would expect.
Old 4 weeks ago
  #29
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enorbet2's Avatar
Quote:
Originally Posted by tigerzilly View Post
Any suggestions to improve. I also notice the trem doesnt have the depth I would expect.
If you mean improve the action of the volume controls I'd recommend moving them AFTER the 1st stage since, as I mentioned before, as they not only exactly and unnecessarily duplicate what you already have on your guitar but they are IN PARALLEL with your guitar's volume control(s) and reduce pickup loading - not a good thing. It would be relatively easy to move to the plates (after the coupling cap of course) and convert to an actual potentiometer.

If you worry this will change response it will but the odds are pretty huge you will greatly prefer the change even though it would be relatively minimal beyond having Volume controls that actually work properly.

For the Trem circuit the easiest way to view it, since the hand-drawn Kay schematic is a bit crowded especially around that Trem circuit, breathe a sigh of relief because it is almost exactly like a Tweed Tremolux circuit (appended below) which is far more legible and also a good point of reference for how much Depth is possible when that circuit runs right.

Obviously the Tweed circuit wasn't perfect or Fender wouldn't have upgraded it and guitarists agree later versions were actually an improvement but the Tweed circuit did work decently and had a decent range of depth just not all the way to the near Off-On levels of the LDR circuit in Blackface amps.

Anyway this is the Tweed circuit that should help you visualize what's going on and what you can check to determine if it is operating properly within spec.

Old 3 weeks ago
  #30
Gear Nut
 

Here's the amp with the new back panel I made. I haven't changed anything with volume pots or trem yet. Still deciding if I like it in its original form. I have a real guitar player coming to test.
Attached Thumbnails
Kay 515 Tube Amp...or is it?-20200831_222438.jpg   Kay 515 Tube Amp...or is it?-20200831_222451.jpg  
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