Build of Triode ST35 Kit, Rev. E

for the DIY ST35, the Dynakit and every other PP EL84

Build of Triode ST35 Kit, Rev. E

Postby whaler » Thu Sep 19, 2013 11:29 am

Hello folks, new kit owner here starting the build. Thought you might enjoy some pictures of the progress. I am sure I will have questions later. The kit parts are still arriving but I have enough to get as far as the pics show.
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Re: Build of Triode ST35 Kit, Rev. E

Postby Shannon Parks » Thu Sep 19, 2013 3:26 pm

Thanks for documenting your build, Whaler. Looking good, and best of luck!

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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Thu Sep 19, 2013 3:44 pm

Shannon Parks wrote:Thanks for documenting your build, Whaler. Looking good, and best of luck!

Shannon

Thanks and great job on this PCB board, I am impressed with the quality and layout. I built an ANK EL84 kit and the PCB quality was very similar, even seemed made by the same company. The Orange Drops did not arrive yet, but I plan to use Jantzen Z caps anyhow. It will take some thought to make them fit.

I am toying with placing the trimpots facing up and drill holes for them on the cover, just not sure how hard this stainless steel is to drill. I would also install tip jacks to do all adjustments from topside.

I will keep the pics coming unless someone objects.
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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Thu Sep 19, 2013 8:24 pm

The Jantzen capacitors arrived today, they are huge. Here is the best I could do to install them in the PCB with limited time. Also, the pots being on topside of the PCB became a must since the caps would have covered them. Now I do have to drill hole for the jacks and the test point tip jacks. I just realized this amp has adjustable feedback, that is great!
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Re: Build of Triode ST35 Kit, Rev. E

Postby snitch56 » Fri Sep 20, 2013 3:37 pm

You may want to cable tie those Jantzen's together to mechanically stabilize them to minimize any possible vibration.
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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Mon Sep 23, 2013 10:47 am

snitch56 wrote:You may want to cable tie those Jantzen's together to mechanically stabilize them to minimize any possible vibration.
Good idea, I did just that with glue, see pic.

Here where I left off last night. Supposedly, the output transformers are arriving today so I can wire everything up. Does anyone know of some good Rev. E pictures for wiring or am I braking ground here?

You will notice in the pictures the holes that I had to drill for the bias trim pots access and tip jacks.
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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Mon Sep 23, 2013 8:16 pm

More pics of tonight's progress. Maybe power up tomorrow. If you see something amiss, by all means let me know. You can clearly see now the access for setting the bias on the topside.
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Re: Build of Triode ST35 Kit, Rev. E

Postby Shannon Parks » Tue Sep 24, 2013 7:03 am

Whaler,

Here's Tom McNally's (http://www.wdox.com, half-way down the page) pics using a Triode chassis and Rev D board:

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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Tue Sep 24, 2013 8:23 pm

Thanks for the photos. Here is where I am tonight. The amp is playing music!! Sound is good, no glitches and the bias was really easy to set topside.
I am starting off with 7189A tubes, but will switch to EL84 tomorrow, it is just too late.

The power transformer is humming more than I like and I hear the same hum in the speakers when the music stops. Other than that, great promise on the sound quality, but too late to turn things up.
The transformer is torqued down tight, but at this level of hum, I can not have it too near.

What do you all think?
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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Wed Sep 25, 2013 6:21 am

Installed some vintage EL84 in tthe amp this morning, dialed the bias in no problem. The power transformer is much happier but still hums quite a bit. This would be no problem other than the same hum is heard from the speakers.

I know some hum is normal, but this hum can be heard quite clearly from the sitting position. Matter of fact, I don't remember ever having, fixing, or building a tube amp with so much power hum.

Any ideas welcomed. I am going to start by swapping the AC line primary feeds and maybe trying a ground lift plug. I also plugged the amp into a power conditioner with the same results.

Other than the hum, the sound is quite good.
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Re: Build of Triode ST35 Kit, Rev. E

Postby TomMcNally » Wed Sep 25, 2013 12:14 pm

Looking good ! I've build quite a few of these (one a couple of weeks ago yet to be posted) and they don't hum.

Things to try ... make up a shorted out set of RCA plugs and power up the amp with the inputs shorted.
If the hum is gone, the problem is before the amp. What are you feeding it with? If it's a preamp, does
it have any connection to ground via TV Cable or a computer with a grounded cord?

If the hum is still there with the inputs shorted, dress your wires to keep any AC away from audio,
including the feedback connections. You might try lifting the chassis ground from the ST-35 board.

Using the terminal blocks makes things easier if a mod needs to be done later, you can remove the
board from the chassis in about 20 seconds.

You might want to grab some stainless steel 1/4" machine screws from the hardware store, it will
make the top of the chassis loook much nicer than the zinc flathead screws, and the chassis won't
get scratched up when the screwdriver slips. :/

... tom

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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Wed Sep 25, 2013 12:57 pm

Thanks Tom, appreciate the advise. My problem seems to be in the AC mains wiring since I placed a ground lift plug on the IEC cord and the hum is gone. I think I need to swap the primaries on the power transformer and maybe do them as you show in this picture, I am sure that will take care of it.

And I will remove the chassis ground from the board, I have never had good results with that. I will leave the chassis grounded unless it gives me fits.

Will post final pics, the sound is quite good even with these old tired vintage tubes. I could not get one of them below 361 mV, there was just no more pot left. All the others, no problem. The 7189 all adjusted fine, so I know it is the tube.

Thanks again.
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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Wed Sep 25, 2013 3:17 pm

OK, hum is gone!

I reversed the power transformer primaries and removed the ground wire to the PCB board.

The only thing I will eventually add is a neon lamp in the front, maybe. Here are the glamour shots. Tom, you are correct about that scratch, it was a slip of the screwdriver. I matched it on the other side and signed the unit in the middle to make it look purposeful rather than a mistake.

Took some advise from my friend DigitalPete and wired the board from underside, I think it looks better. I can actually still access the underside somewhat. As much as is possible I stray from connectors.

Thanks for the help.
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Re: Build of Triode ST35 Kit, Rev. E

Postby Shannon Parks » Fri Sep 27, 2013 4:59 am

Thanks for all the picture uploads, Whaler! Looks fantastic and you should enjoy that amp for many years.
BTW, I also used Adcom preamps with my ST35s over the years.

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Re: Build of Triode ST35 Kit, Rev. E

Postby whaler » Fri Sep 27, 2013 11:14 am

Shannon Parks wrote:Thanks for all the picture uploads, Whaler! Looks fantastic and you should enjoy that amp for many years.
BTW, I also used Adcom preamps with my ST35s over the years.

Shannon


...and thanks for the help and the great design of Rev. E. This is really a nice board and kit, it performs way above its price level. Very simple to build and the instructions are great. The Adcom seems to be a great match for it, but you ought to hear it with my John Curl 2 clone, they are producing some magic together.

Yesterday I placed some beefy Russian top military spec 6p14p-ep tubes in place of the EL84, and WOW, the bass is amazingly strong and clarity is plenty. Imaging is very focused and deep. These are cryogenically treated tubes, so they are supposed to be top audio performers. I am getting all this without the amp even breaking in, better things are even to be expected when broken in.

If anyone is wondering about how good this amp sounds, wonder no more. What a gem find it is!

Here is an EL84, 7189A, and 6P14P pin comparison that might be useful for some.
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