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Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Sun Dec 01, 2013 5:49 pm
by whaler
The amp has been playing stellar until today, it just went silent. Checked the fuse, blown. New one in, same thing.
Took all the tubes out, tested them all on my Eico. All are in really good condition.

Tried turning the amp without the tubes, immediately a roar from the power transformer and the fuse blew, no tubes mind you.

Looked inside, no evidence of stressed components anywhere...

Power transformer bad? HELP!

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Mon Dec 02, 2013 5:57 am
by Shannon Parks
With it powered off and well drained (sitting for ten minutes or so):
1) Disconnect J1-1 and J1-2.
2) Check D1 and D2 with a DMM set to diode checking mode. Look for an open one direction and around 0.7V the other.

If the diodes look good, I have more tests for you. If one is bad, then go ahead and replace both. And use four - two in series for each diode. This will give us twice the voltage protection. Also check for a shorted (failed) supply capacitor, but usually it's a voltage spike that kills the diode.

Shannon

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Mon Dec 02, 2013 4:27 pm
by whaler
You were right on the money, one of the diodes is voltage dropping in both direction, .218 one way and the other .198, the other diode is OK.

I went to Radio Shack and totally forgot to get them. I have a bunch of 1N4004 laying around, but I think these are borderline. BTW, in my troubleshooting yesterday, I had remove the secondary b+ from J1, 1 and 2, and the amp powered up fine with just the heaters running. The power transformer was quiet.

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Mon Dec 02, 2013 4:51 pm
by Shannon Parks
I think an occasional spike from the on/off switch creates a large spike which can be greater than the 1000V reverse polarity rating of the diode. Probably we can stick with single 1N4007 at U1 and U2, but need something like .047uF, 250VAC across the on/off switch.

Shannon

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Mon Dec 02, 2013 6:48 pm
by whaler
Another clue, the black thermistor, or inrush limiter was cracked like it wanted to burst open. A little tap by the finger and it broke. I had some spares so I replaced it already.

I probably have one of those AC caps on a donor unit for the switch, let me look around. If not, I am back at Radio Shack tomorrow for the diodes anyways.

Thanks!

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Tue Dec 03, 2013 8:59 pm
by whaler
Thanks Shannon, your initial diagnosis was 100% correct. The diode was the problem. Probably took a surge. Went to Radio Shack and I got the combo rectifier diode pack with four 1N4007 among others. These all went in as you suggested. Powered up without tubes, no problem or noise! Proceeded to add a switch to connect ground chassis to signal ground in one situation where the preamp needs it to quiet down. See the picture for that, the switch mounts next to the speaker connectors with blue wires. Also, notice the new inrush limiter (black round ceramic disc).
The amp performed stellar again for a couple hours tonight.

Thanks for the expert advise!

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Wed Dec 04, 2013 5:27 am
by Shannon Parks
Excellent! Glad it a cap didn't get damaged in the event. A couple comments:
1) I can't tell from your picture, but make sure that D1 & D2 are two diodes in series, not parallel. Just making sure. ;)
2) Push that CL90 away from the cap.

Shannon

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Wed Jun 11, 2014 11:34 am
by ro7939
Greetings all!

Has anyone compared this kit to point to point wired EL84 kit? I have no dog in the PCB vs. point to point fight, just curious. Obviously I'd prefer a PCB kit for it's assembly ease. OTOH some believe point to point wiring sounds better.

All associated components, speakers, and my large dedicated treated room are exemplary. So this application will display the smallest differences between amps of different quality. Speakers are 93 dB, 8 Ohm flat above the bass range, 6 Ohm minimum, low-moderate phase angle, and bass cutoff high 30 Hz range. Active powered Distributed Sub Array employed below 40 Hz.

Jimbo

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Wed Jun 11, 2014 7:28 pm
by paart
Who sells a "point-to-point" wired El84 kit?

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Wed Jun 11, 2014 8:59 pm
by corndog71
He might be referring to mine which I'm not selling.

Image

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Wed Jan 13, 2016 10:08 am
by jcfardo
Hi whaler

Are OTs Z565-48?

Thanks

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Thu Jan 11, 2018 10:57 am
by henniekuyper
Good day everyone.

I saw this post, and this is really a nice looking amp!!

What is the dimensions of the chassis?

Kind regards
Hennie :{)

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Fri Jan 12, 2018 6:50 pm
by nyazzip
my chassis measures about 33 x 24 x 5cm

Re: Build of Triode ST35 Kit, Rev. E

PostPosted: Fri Apr 10, 2020 11:30 am
by chrx
Finally getting back to my ST35 kit build, with the extra “commute” time I have while working from home now.

I got these steel hole plugs from G.L. Huyett, to cover the extra holes in the top for access to R19 & 22 and R25 & 28:
https://www.huyett.com/Products/Fastene ... 8152-K1110

They look nice on the chassis and come in 1/2” and 3/4”, which work well for this application, as well as other sizes.

Cheers, chrx