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Post subject: Re: Terry Kath Amp
Posted: Thu Nov 17, 2016 10:46 am
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Yes, my schematic improperly shows the HV caps connected to ground.
However, I drew this schematic making assumptions about standard layout before I repaired the amp.
When I repaired it and fired it up, I had to reevaluate the schematic because of the high power it put out. I never documented the changes after I discovered my error.
Look at the underside at the cap wrapped in orange tape. The ground of the cap plainly goes to a yellow wire to a 5Y3 tube for a stacked B+ of 630VDC.
That accounted for its capability to produce 70 watts with just two tubes.
The customers request was to keep the amp in as original condition as possible. Rewinding the OT was out.
I was lucky as the burned windingd were at the edge of the core.
After cleaning out the burn, I found three windings I could use. They totaled in resistance just 10 ohms less than the other side.
I twisted and soldered them together. Then I filled the entire void with silicone. I let it cure for two days before firing it up.
I let it run for an hour or so with some music on new tubes. Then I installed the old tubes. The bias was the same and I let it run for an hour with no problem.
So I think as a museum piece, it should be OK until the caps start to go. They looked pretty good to me, so I expect it'll run for a good long time.
The Bogen amps are very similar to these. I just got one in that a customer pulled out of a dumpster in Nebraska. But I haven't seen a Bogen that comes close to this power rating.
I'm still not sure where they got the 150 watt peak rating. Maybe in 4 ohm. It sure won't do it in 16.


.


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Post subject: Re: Terry Kath Amp
Posted: Thu Nov 17, 2016 11:37 am
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Awesome, awesome job! I'm sure a working amp, as a museum piece is much better --- than a non-working piece. Even if it only gets used once every 6 months or longer. Bringing back historic R&R equipment is a worthy cause.

BTW.. have you seen the series currently on PBS , "Soundbreaking?" Pretty neat stuff.

http://www.pbs.org/soundbreaking/home/

Gonna put on Chicago first album CTA --- drink a couple of beers. :)


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Post subject: Re: Terry Kath Amp
Posted: Mon Nov 21, 2016 8:29 pm
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TimsAudio,

If you have final photos of restored amp, I'd love to see them.

:mrgreen:


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Post subject: Re: Terry Kath Amp
Posted: Mon Nov 21, 2016 9:11 pm
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I would love to see it shiny and new looking, but my instructions were for a minimalist intervention. I even left the spider webs.
I did tension the tube sockets, clean tube pins, clean controls and grease a slide switch. Mostly unseen items.
It was delivered to the museum only 2 weeks before the induction ceremony. If it is deemed significant enough to include in the display, I imagine a museum restorer with much more experience than I will do the work. Otherwise it will just sit in a closet again. I'll never know.
The damage to the plating was apparently from a drink or spmething. It's corroded through the plating. Its far beyond my capabilities to repair that. The original color still looks good on the bottom, kinda goldish bronze. I have no idea how to replicate that
.I'm better at makin stuff work than makin stuff pretty.


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Post subject: Re: Terry Kath Amp
Posted: Mon Nov 21, 2016 11:27 pm
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Tim,

Vintage amp with all the patina is cool. IMHO.

:)


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Post subject: Re: Terry Kath Amp
Posted: Sun Nov 19, 2017 4:26 pm
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This is my first post to the forum. Please forgive my ignorance to any protocols that I may not yet be aware of.

As a devout follower of Terry since CTAs first album was released in 1969, I was beyond thrilled to discover your post today regarding his amp. I have been a lifelong tone seeker of Terry's (I am now 62) and until just last week was still under the impression that his sound was produced by some combination of a Bogan CH18 and a "dripedge" era Fender Dual Showman.

After watching the premiere of the documentary "The Terry Kath Experience" produced by Terry's daughter Michelle Sinclair (airing on AXS two weeks ago) I was inspired to redouble my efforts to learn more about Terry's gear. I the process, I came across a YouTube video of a gentleman by the name of Nick Morrone, who claimed to be friends with Terry and said that the amp in the video, had been given to him by Terry, (I believe) (https://www.youtube.com/watch?v=-_R9rW_inGs).

After some additional research, I deduced the amp in the video was probably a Knight KN3275C. I quickly scoured the internet and found one for sale, which I just took possession of Friday. While it was sold to me from a reputable source, and represented as a working, restored piece, I am preparing to pop the top off and have a look around before testing the tubes and firing it up.

That brings me to today, when I was doing some more research and I came across this post. As I read down, I discovered I would be required to pay a $400 annual subscription fee to Photobucket in order to see the images you had posted of your restoration project. Is there any other way to see these pictures?

Thanks for all you have posted. Today has felt like I have finally come to the end of a decades long journey.


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Post subject: Re: Terry Kath Amp
Posted: Sat Nov 25, 2017 11:25 am
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Yes, the amp I posted about was Nick's.
While I still have the photos, I haven't figured out a new platform to host them on.
Still, the mods to replicate the amp were surprisingly simple. First, it was set to 16 ohm output.
The two shielded input wires were both wired to a single 1/4" phone jack. This gives two gain circuits for lots of dynamics.
The input load resistors were changed to 1meg from a higher value. I don't remember if the originals were 3.3 or 4.7 meg for the original mic. 1 meg is more suitable for guitar.
And that's it.
This amp uses very high b+ voltages. Be very careful when discharging. There are two seriesed supplies that both need to be discharged separately. But that is how it gets 70 watts out of two tubes.
You can dm me here with an email so I can send pics


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Post subject: Re: Terry Kath Amp
Posted: Sat Nov 25, 2017 9:47 pm
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I have been following this one from the beginning, such a cool story and repair, thanks for sharing.
mud


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