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Post subject: Terry Kath Amp
Posted: Tue Nov 08, 2016 11:10 am
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This is an amp that came through this March. I believe it’s the real McCoy.
I’m sure there are many who know much more about this story than I do.
A childhood friend of Terry Kath brought it to me. He said he bought it when Chicago was clearing out a warehouse. He wanted it repaired for submission to the R&R Hall of Fame in April. It was a challenge and an honor to do it. For those of us that will never make it there, here’s a peek under the hood of this legendary music maker.
There are three items that detail the provenance of its history.
First is a U tube video of the amp in action.
https://www.youtube.com/watch?v=WmOEwiz5Kxs
Second, the video also shows the distinctive Pignose knobs. Terry was apparently the founder of Pignose.

Third, The note taped on the side of the amp indicates that this is the number 3 unit. So this amp may not be the amp actually shown in the video. The linkage is unmistakable though. I believe one of the hottest pickers on the planet tweaked this amp, that you would normally find on the Principals desk, into a unique Rock n Roll powerhouse.

It’s a humble looking amp. The distinctive Pignose knobs are heavy castings. The damage to the original bronze plating was probably from a spilled cocktail.
The starting point is a Knightkit PA amp from Allied Radio. The date on the OT is from 1964. It runs two EL34s with a 650 volt plate for 70 watts output.
I was excited to peer into what was hot rodded and was surprised to find very little changed.
The two mike input jacks were removed and wired to a single ¼ “ jack.
This gives two input preamps to dial in huge amounts of gain.
The input load resistors were lowered from 3.3M to 1M
The output impedance was set to 16 ohms. That’s it. No tone stack. No reverb. Nothing but clean tone and magic fingers.
Image

This is the bare chassis.on first opening it up
Image

This is the bottom side
Image


This is the OT damage. The secondary was fried. I went in with a Dremel tool until I hit copper. I cleaned out the burned paper and pulled up the wires that showed. Using an ohm meter, I found windings I could splice to make a more or less complete winding.
It actually worked. It’s not something I would take gigging, but for a museum piece, it’s OK.
Image




Ptransformer
Image

OT date
Image

tape side
Image

So, What’s it sound like? Well, not being a picker I never plugged in a guitar. With rock n roll played through it, it was a ballsy, dynamic amp with clean tone throughout.
But just spin some old Chicago and commune with the spirit of Terry Kath. It was good for me.


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 08, 2016 12:14 pm
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ARE built some pretty stout stuff, up until they merged with or were bought out by Tandy in the early '70s. I remember their tube power amps as being clean, loud, almost linear in their sonic reproductive capabilities. IIRC they were quite similar in circuitry to the Dynaco gear of the era.

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 08, 2016 12:19 pm
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Very cool, thanks for the post. It is nice to see some history
mud


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Post subject: Re: Terry Kath Amp
Posted: Thu Nov 10, 2016 5:04 pm
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Pretty tidy for a point to point....thanks for the pics.


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Post subject: Re: Terry Kath Amp
Posted: Sun Nov 13, 2016 10:33 am
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Awesome amp! Notice how it has two rectifiers? A 5Y3GT to drive the gain stage. And a GZ34 to drive the EL34 output stage.


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Post subject: Re: Terry Kath Amp
Posted: Mon Nov 14, 2016 10:37 am
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The power supply is an odd one.
Near as I can figure, the secondary winding for the power stage is bootstrapped to the power supply for the driver stage.
So the negative of the high voltage filter caps is connected to the B+ of the driver stage. I've seen an old sears 1428 amp wired this way.
This is how they get enough plate voltage to get 75 watts out of 2 tubes.
I'm not surprised the OT went South with that kind of B+
The amp is listed in the 1965 Allied electronics catalog page 344 for only $84.50. The catalog shows a painted cabinet. I don't know where he got this finish.
Maybe its a showroom piece, but the burnished gold plating on this one still looks good on the bottom. Restored, it would look awesome.
http://www.alliedcatalogs.com/catalogs/1965-240b/


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Post subject: Re: Terry Kath Amp
Posted: Mon Nov 14, 2016 2:49 pm
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Sure would be nice to have a schematic of this amp. Maybe, it has voltage doubling caps in the PSU?


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 15, 2016 10:23 am
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This is the schematic I drew. The red circles were where I thought the mods and previous work were.
It doesn't show the stacked PS like I thought. So many amps its all a blur. I'm not sure if the grounding scheme would work in a stacked PS. So at this point, your guess is as good as mine.
But perhaps you can make the determination from the pics of the underside.
I seem to remember that it put out more power than expected. It also had a higher plate voltage than expected. I think I discovered the stacked PS after I made this drawing.
I would expect that there is a Sams fotofact sheet with the schematic somewhere. The B model claimed the same power specs.


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 15, 2016 11:04 am
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Thanks, for the drawing. There are no voltage doubling capacitors, that I can see.

Where is the line going from the 5Y3GT, after its PSU section. Looks like "OT 63?"


Thanks!


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 15, 2016 7:30 pm
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I think it says OT center tap.


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Post subject: Re: Terry Kath Amp
Posted: Tue Nov 15, 2016 7:54 pm
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Tim, I don't think that is correct. The CT of the OPT has B+ label. B+ is off the GZ34. BTW... the "S. grid" tap is off the wrong point. Should be "C" point. The screen voltage should be lower than the anode, for them to work correctly.


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Post subject: Re: Terry Kath Amp
Posted: Wed Nov 16, 2016 9:02 am
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I send this amp up the flagpole, on a DIY Board. See if anyone salutes it. :mrgreen:

In this photo, I believe there maybe two similar amps, stacked behind him.

http://pulmyears.files.wordpress.com/20 ... kath74.jpg


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Post subject: Re: Terry Kath Amp
Posted: Wed Nov 16, 2016 11:16 am
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That sure looks like em.
Looks like the schematic can be had for $15 from Sams. Its item 91752 for the B model. It is slightly different, but the power stage specs are the same.
That could clear up my faulty drawing.


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Post subject: Re: Terry Kath Amp
Posted: Wed Nov 16, 2016 11:50 am
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Tim, SAMS is the way to go. I'd love to see that schematic.

After reading stuff on the Net, modified Bogen PA amps have been associated with early Terry Kath touring gear. But, this maybe a strong case of mistaken identity. Your amp's dial arrangement APPEARS to be closer to the ones used by Kath. Esp, if you look at how Bogen dials and front panel switches were arranged, at that time.

Since you got it from what looks like a trusted source (childhood friend) --- amp could have a lot of historic significance. Well worth restoring to working order, if possible. Have you seen any other PA amps associated with Kath? My bet, is this maybe the only potentially working one still around.

Good luck on your endeavor! :)


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Post subject: Re: Terry Kath Amp
Posted: Wed Nov 16, 2016 4:16 pm
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Knight KN3060 schematic. Close to the KN3275B.


EDIT/UPDATE #2: One 5Y3GT. One 5U4Gb (or 5AR4). Two EL34 output tubes. No interstage tranny. Two conventional PSU setups. Supplying voltage for two different stages of the amp. No voltage doubling or other unconventional arrangements.

The 5Y3GT rectifier powers a 410VDC source. For the gain & EFX stages. The 5U4GB or 5AR4 powers a 610VDC source. Knight gets this high voltage by putting 940 PIV voltage onto the anode plates of that 5U4GB. Both 5Y3GT (600 PIV volts) & 5U4GB (or 5AR4) are driven hard, by this amp. It maybe very difficult to find a new replacement tranny. May need to be rewound, if you want this to be a working museum piece.

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