Enter the Tweed, or, How I Learned To Stop Worrying And Love The High Power Twin

You know how sometimes you get a wild hair and decide you want something really outlandish? This is what I ended up with and thereby hangs a tale.

One time I stumbled over some of Hartley Peavey's musings about some of the amps he'd built over the years, one of which was the Peavey "Vintage" series. The very early ones were all tube and they're kind of hard to find. I've only seen pictures of them, and they included a 2x12, a 4x10, and a 6x10 towering monster. All three were 100w of all tube power including the out of production 6C10 triple triodes.

What you had, essentially was a 100w tweed Bassman with reverb. Now who wouldn't like that?

I couldn't find one for love or money so I said to myself "Well, I'll just make one, won't I."

So I got in contact with J.D. Newell and he figured he could cook up a 4x10 cabinet that could house a High Power tweed twin chassis.

Somewhere along in there I acquired a chassis and transformers from Mojotone and started constructing the chassis.

I also acquired two new Eminence  Legend 12 inch speakers on the recommendation of a friend of mine. About then the project became a high power tweed twin. I built the eyelet board and sourced the parts, most of which I had and built about 90 per cent of it, and the cabinet and speakers were sitting in my living room.

I used quality parts throughout, Heyboer  iron, F&T and Mojotone capacitors, and choice power and rectifier tubes from my stash: a Mullard rectifier and RCA black plate 6L6GCs.

I also incorporated some changes to the screen and grid resistors. After the first run I changed the Switchcraft jacks for Cliff jacks with a substantial reduction in noise.

All was assembled including a bracket to support the power transformer. It saves a lot of effort to assemble this amp upside down.

How's it sound? Loud as hell, but the speakers are not broken in at all. It sounds purty bright but will mellow with time.

On to  the next project-reviving my Marshall Club and Country. Stay tuned.

There matters stood until last weekend when I finished the wiring, adjustable bias control, and jacks. The first run was uneventful.

UPDATE: I've found some follow on buzzing that appears to be circuit related so it'll have to come out and get on the scope to locate the source of discomfort. Stay tuned.

Tube matching to the Max: The Maxi Matcher cometh.

I've been hankering after a Maxi Matcher for a while. It's a stand alone tube tester and matching device for certain power tubes and it's fast becoming the standard for the industry, so I thought I'd get one. Keeping up with the competition and all that.

I figured it was also a good bet for matching anything but KT88s and 6550s, as those I will still use Iron Gertrude for. That's my home brew tube matching device, it's completely analog and what's important is it'll put out 650v when called upon without even breathing hard, which is mandatory for high voltage Ampeg productions.

In any event the $695 was coughed up and the tester arrived here today.

Right away I knew something was wrong, and it is either me or the tester.

Doing the setups per the instruction sheet in the lid of the nifty hard plastic case I pulled a set of new Shuguang EL34s off the shelf, set the plate voltage to 400v, set the bias to -36v and proceeded to read the outputs.

The plate current should have been between 21 and 50 ma, and the transconductance should have been  greater than 4.0. What I got was around 6 ma per tube for plate current and the transconductance was between 1.76 and 2.31.

This was not good so I pulled another set of EL34s out of their boxes, this time a new set of JJs. The results were quite similar.

That got me worried. I measured the filament voltage and it was about 3.4vac, not the 6.3v one might expect. The 350v and 400v plate settings yielded  177v and 212v respectively.

I'm not convinced that the transformer output voltage is correct and I suspect that it has a 240v power transformer installed.

I'll keep you posted but until I hear back from the makers it's an expensive piece of eye candy, and I'll be using Iron Gertrude for my matching chores, as fussy as she is.

Stay tuned.

UPDATE:  I got a call from the folks at Maxi Matcher and what they told me was that they use a dual winding power transformer that is suitable for 120 or 240v depending on how it is wired. I got an email detailing how to switch the necessary jumpers.

In the lower left hand corner of the circuit board are  three places for jumpers. Bridge the inner one and you have 230v. Remove that and bridge the outer pair and you have a 120v transformer.

Smooth, Very smooth.

Rather than dismounting the circuit board I sweated out the existing jumper and installed two other jumpers-they look like staples-made from the wire shaft of a resistor.

It was easy enough to do and now it works just as it should, and the socket voltages bear witness to its proper function.

It still can't deliver the plate voltage that Iron Gertrude does, but it is quite a bit more stable and the digital readout is good for us old folks who tend to squint a lot.

I tend to think I'm going to be using this a lot.

UPDATE 2: I recently had a Blackstar HT60 in for a high volume crackling that it exhibited. The first task was to put the TAD EL34s -a/k/a gussied up Shuguang-on the Maxi Matcher and after about a minute of cooking the overcurrent LED illuminated and things shut themselves off as they are supposed to. This was a fault I could not have detected on my Hickok tube tester. A reboot confirmed this. A new set of EL34s from JJ and everything was peachy keen, no more unwanted crackling and distorting.
So score one tough fix for the Maxi Matcher that was worth it alone for what I paid for it.Colleagues have reported similar occurrences so I'm on solid ground here.

This is the second set of TAD EL34s in Blackstar amps that have failed or otherwise exhibited bad behavior recently. As of this moment they are all suspect and I'm not buying any.