New spin for ST-35 Design

Oldtube

I'm getting closer. Relief seems to be on the way.

I noticed that the populated board on Ebay is rev 0. The unpopulated board is rev 2, which specifically calls out Auricaps. What is the difference, or is it just photo updates?

Thanks,

Alan

Hello Alan,

We start designing the ST-35 with Giuseppe circuit incorporated (1 Bias control for all EL-84), and I put Rev 0 on it. Then we decided to create the ST-35 without bias control, where you have to adjust one by one EL-84 bias control, and I kept Rev 2 on it.
Both are great circuits; this is all about preference. Some people prefer to adjust bias individually. The Giuseppe circuit claims also that by using his circuit the bias current is reduced, meaning by each EL-84, so less heat, and less power consumption. In the end he claims that is also less distortion.

This is the difference between them. The populated is my last of this lot. The unpopulated we still have 4 left over from this lot.

I let you to decide. Last point is that for sure the populated you are going to save money, since components went up $$$, but I put the cost of when it was populated.

Enjoy!

Hi OldTube,

Can we talk about a custom arrangement? My username at gmail.

Thanks,
Alan

Hello Alan,

Please post pictures of your assembly if you can.
This will be great to see it.

Thanks!

I got the amp working.  The wood case and chassis are very nice and the amp sounds great - but I have some hum that I haven’t tracked down yet.  It is not loud.  I cannot hear it at listening distance on 90db speakers.  But on my 95db horn speakers, I can barely hear it from listening position.  I suspect it’s my sloppy wiring.  I did not separate AC from DC carefully, and I did not take care to route the signal - level wires away from others.  And I did not have any shielded cable for the signal wires, so I just twisted hookup wire. Luiz thinks it might be a ground loop involving the back panel and the top panel.  I like listening to it as-is so I haven’t been as aggressive as I should be about diagnosing the problem.  I’m planning to use it with Halcyon speakers (Curt Campbell design), but haven’t hooked them up yet.   The picture below was taken with the tubes set too hot, before I got the bias set properly.  The tubes don’t glow like that now, but I like the look, particularly at night.  

Hello Alan, this came like a beauty! Very nice looking!
Yes, we just need to figure out the hum. The very first I've built I was playing with earth connection between the back plate and the top plate to remove the hum. I was able to remove it when I removed the earth from back plate. If that does not help, it could be the 60Hz frequency picking somewhere due to cable routing.
I'm happy you are finally enjoying it! The EL-84's sounds fantastic!

Let's see how we can eliminate that. It should be pure and clean sound without the ham.

Last night we did some tube rolling of the 12AU7. I had a GE 5751, a basic Amperex, an Amperex Bugle Boy, an HP medical, and a Mullard. Consensus was that anything Amperex was the best for highs, vocal clarity, and strength (dynamics). However, the GE 5751 was the crowd favorite. Lower volume, but smoother, warmer. It took the edge off, which we needed with my open baffle 97db speakers. With lower sensitivity box speakers, the Amperex were preferred. Bugle Boy price premium was not appreciated vs regular Amperex.

And I’ve been getting lots of compliments on how nice the amp looks. Females seem to like it.

BTW, if anyone is interested in building this great-sounding and attractive amp, there are some boards still available on eBay and Luiz still has at least one chassis.

https://www.ebay.com/itm/225774263966?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=wzZzolA2RqW&sssrc=4429486&ssuid=hzPANM_6Rl2&var=&widget_ver=artemis&media=COPY

Also got a chance to test some 12AX7's with people who have good ears and good musical sense. The candidates were a plain Amperex 12AX7A, a Telefunken (1960), a Sylvania, an RCA black plate, and a Hammond-labeled Amperex bugle boy.

The Telefunken won by a country mile, followed by the Hammond/Amperex.

BTW, the output tubes I'm using are Russian 6P14P-EV by Reflector. 1958. I don't have anything to compare them to as I never bought any JJ's or anything like that, but some people did some EL84 comparisons online and they liked these 6P14P's a lot. They came from Ukraine and cost $50 for matched quad. Ebay said they would take 2-3 months to arrive, but it got them in 2-3 weeks. I ordered another set of the same tubes and they also took 2 weeks to arrive from Kiev.

Next experiment is with some Bendix 6094, which are also very highly regarded. They need an adapter. Hard to find at a decent price, it seems.