I think some DuMont TVs used that 6AL7 as a tuning indicator on their Inductuner models.

I'd like to see one of those, Brian. I haven't been around any old-time TV's since my bench apprenticeship during junior-high summers, back in the mid-60's.



Larry

I gave this type some notice in an earlier entry when I had some trouble with a 5691 equivalent to one, but like the 6AF6G, it deserves more attention, since it isn't nearly so well known as the tube it replaces (6SL7GT).

These are the three power amp chassis front end tubes in BB. Two of them ordinarily wear copper shields.



The 6SU7GTY is one of several Tung-Sol proprietary winners. The 5881 and 6550 are two others, and two that made it into manufacture by others. Apparently the closest anyone else got to the 6SU7GTY, however, is the 5691, which is a close equivalent.

In fact, the 5691 in this view appears to be a duplicate:



The 6SL7WGT (Sylvania) is probably the next closest equivalent, and two of those, with their brown bases, can be seen in the rear row of tubes behind the 6SU7 trio.

The 6SU7GTY is to the 6SL7GT what the 7025 is to the 12AX7. In fact, it's not an exaggeration to call it "the octal 7025."

It's a plug-and-play replacement for the 6SL7GT with a low-loss micanol base (this helps improve the noise and signal loss factor). It carries Aquadag electrostatic shielding on the inside of the bulb. It is also tested with AC on the heaters for a low hum-and-noise characteristic, and it is tested for balance between its two triodes.

I have experimented with several "marks" of this tube (from World War II through the late 1950's) over the years, but the "mark" you see here (1951 vintage) is far and away the best-performing version I have encountered.

It is somewhat microphonic if the micas are not snug against the glass, but earlier and later marks can be far worse.

They also tend to show up much worse for hum and noise. The 1951 mark seems much slower on average to develop heater-cathode leakage than other production runs (some later 1950's editions developed it fairly quickly!).

In this 1951 mark, it seems, they got everything as good as it gets with this type:



I first got acquainted with this tube during high-school years, via my former boss, on whose bench I had apprenticed for two junior-high summer seasons. He was an old Signal Corps vet, and he had many boxes full of WWII surplus tubes (wish I had them now! ). A number of these 6SU7's were among them. I was able to get half a dozen to start with, and I built my first project with these tubes in 1967.

For some years thereafter, they weren't hard to find, and they weren't pricier than ordinary 6SL7's. I found a number of them at RARSfest in the late 1970's, and got several more from Fair Radio at about the same time.

These days, of course, things have changed, as one look at any "mark-1951" 6SU7GTY's on the "auction site" will show you (the asking prices are egregious these days!) . I'm just glad I discovered this tube when I did, and stocked up on it long ago.

All the best to one and all ,

Larry

I just realized that I left something out of the last post.

In describing the 6SU7GTY, I really should have said something about "black plates," or something of that sort.

That would have titillated all the usual suspects, and I always like to do a good deed for the day....



Larry

I have to get "psyched" for a gala keyboard affair tomorrow night.

At such a time, I have to remind myself of the nature of my calling, put synths and samplers aside, and dial in my native instrument, the piano.

The nice thing about a quality piano recording is, it'll show up deficiencies in a sound system like little else. It's particularly likely to show up phono cartridge deficits, to begin with, and certain kinds of distortion farther down the line.

Listening: Ravel, Concerto in D for the Left Hand, John Browning with Erich Leinsdorf and the Philharmonia Orchestra, Capitol SP8545.

This disc carries Prokofiev's 3rd Piano Concerto in C on the flip side. It dates from Capitol's "spectrum label border" period (1961).

Paul Wittgenstein, a Viennese concert pianist who lost his right arm in World War I, commissioned a series of works from distinguished composers, and this concerto (1931) is one of them.

It is pure vintage Maurice Ravel, witty, sophisticated and urbane, including jazz impressionism and vivid contrasts. To quote the liner notes:



I can only observe that at times, it appears that the pianist must be using two hands to get the job done .

Apart from that, it's a devilishly clever and elegant work (Stravinsky didn't refer to Ravel as a "Swiss watchmaker" for nothing). And it's more than a little delightful to hear a bassoon playing a theme Gershwin might have written (complete to bending notes, blues style, here and there). A great mood shaper, this one.

Cheers and St. Pauli tonight,



Larry

Hmmmm!

Those new 7027A's have enough hours on them now to start glowing blue-violet around their bases. They didn't glow when they were new, but they have about 40 hours on them, and the glow is very obvious now.

There's no change in performance that I can detect, however, which is good, for there isn't supposed to be.

This is a topic that's come up often elsewhere, and it might be a good idea to revisit it now.

This is the "flourescent" glow that dances in time to strong signals coming through the tubes (there's another kind that shows up only within the plates of certain power tubes, 7591A, 7868 and such).

This blue-violet "dancing" glow is caused (reportedly) by stray electrons striking the glass (although how they can get that far out, with that big plate close by to pull them in, I've never understood).

I also don't quite see how it can be a function of aging, but it obviously is, in this case. Vaporization of materials maybe? In any case, I'm going to keep watching the bloom.

Listening: Men of Brass, massed British brass bands of Foden's, Fairey Aviation and Morris Motors, conducted by Harry Mortimer O.B.E., London FFSS PS-101.

This disc is a feast for those who like British brass band music, especially of the old school. Stylistically, these bands have changed noticeably since the time this album was recorded (around 1960). For one thing, there was a strong emphasis on vibrato in the old days, and you don't notice it so much nowadays.

Three championship bands got together with Harry Mortimer, the legendary brass band champion and conductor, to make a couple of albums for London, and this is the first of them. It was recorded in the Belle Vue Gardens in Manchester.

Many traditional brass band favorites are here (Cornet Carillon, Bugler's Holiday, Mill in the Dale, Queen of Sheba Grand March, Espana Cani, Introduction to Act III of Lohengrin, and the 1812 Overture are all here, along with other selections).

The mikes are set well back from the bands, so they "stand back" and don't blast out in your face. This also allows the parts to blend and thus adds to the overall ensemble effect.

The 1812 is an abbreviated arrangement (a good deal of the middle development is notched out), and there aren't any cannons, but it is still a bravura performance. So is the entire disc.

Cold 807's and hot 7027A's tonight!

Larry

I like seeing the pics you have of that amp in the dark.
So is that real indicator lamps with bulbs or did you replace with LEDs inside?

I've always liked those on older equipment. I suppose the sources for the panel indicator with the colored lenses have pretty much disappeared.

Yes, Mark, BB does look a little intimidating and foreboding in those pictures . I'm glad you like them.

Most of her lamps are real indicator lamps. Some are neon and some are incandescent. Then there are the three magic eyes and the two-inch blue scope tube (2BP11).

No LEDs anywhere.

The best place to find old-fashioned lenses and socket assemblies may be a good-sized hamfest. RARSfest is coming up here Easter weekend, and it will certainly be worth attending if you can make it. I'd be vastly surprised if you don't find at least a bucketful of such things, along with lots of other hard-to-find parts and assemblies. A lot of guys deal such stuff around here.

The big thing at hamfests around here nowadays is liquidators doing grab-bag sales. They bring in boxes and boxes of parts, hardware etc. and give you the choice of filling up dollar bags, five-dollar and ten-dollar bags etc (quantity unlimited while supplies last). They also sell a lot of larger parts one by one.

A lot of tube dealers will be there too, ESRC among others.

With all the tekkie guys we have around here, a lot of flea-market stuff always shows up. That includes many old radios and boatanchors (some untouched, some reconditioned), vintage and reconditioned test gear, and vintage TVs and hi-fi gear too. I know a guy who walked out with a Mac Sixty for $25 four years ago.

When I found that out, I could have just screamed.

Larry

For those who came in late:



Never bring a popgun to an artillery duel....



Larry

A man after my own heart! Why use 5 tubes when 56 will do the job!!! Great piece of work there,

As a designer I can appreciate the work invested and the satisfaction of getting the results. I also built my own audio system, albeit mine is solid state and resides in an equipment rack in the basement because it doesn't fit in the living room!(120 W RMS / channel + 200 W sub woofer center channel.)

Long Live Home Brew!

Many thanks, CaveRat, and welcome to the Forum !

It is GOOD to find another full-blown homebrew audio man. Congratulations on your system, and I hope you can supply us with some pix in a thread about it .

Yes, units like these represent a lot of work, with a lot of trial, error, wrong turns and bad language. But there is absolutely no feeling that rivals the satisfaction you get when you finally complete the job, and you witness it doing what it is supposed to do.

To be perfectly honest about my own case, it started out in 1976 as a project, but over the years it became very largely a rite of passage, a testimonial of self-validation. "I am, because I DID." See where I'm coming from?

Homebrew has a good home here, much of it being homebrew receivers and transmitters. You'll see some very elegant and well-turned productions here, and I look forward to your own contributions.

Best regards, and again welcome .

Larry

BB is pushing 500 hours runtime and testing now, and I'm getting some ideas about some corrections in the mixer chassis.

Although it matches my keyboards fairly nicely, it isn't quite as "bright" as the old one was, and I miss that. I have a fair idea about where the corrections ought to go, and it shouldn't take long, provided that I can find the time to get started.

April's a busy month.



Larry

Hi Larry, sorry to go OT but here goes. I just wanted to catch up. I am in Melbourne Australia until May 2 so April is busy for me as well. But for a different reason. Glad that you are still busy with firebottles. I have limited access to the Internet here and it is expensive. You pay for every byte uploaded and downloaded.

Cheeres,

Double post again....

Larry

Good grief, Don, they're tight, aren't they?

But it's good to hear from you all the same, and I hope you're doing well and will soon be back with us. Take care and have a safe journey home .

Larry

Thanks friend. Things are coming together slowly but everything is on target. Will check back when I can. Keep the valves warm for me!

Will do .

RARSfest coming up in a couple of weeks. I'll be looking for some more valves then, among other things. Wish you could visit us! It's always a lot of fun and it's a growing hamfest.

Larry

RARSfest was great, as witness:

http://www.virhistory.com/ham/rars-11.htm

Just stumbled over this link today; squirreling it here, where I can be sure of laying hands on it. Believe it or not, they even snagged a picture of yours truly .

I will be returning to this BB project soon. I MUST get several other chores on the bench and off first.

Kindest regards to one and all

Larry

Glad I was NOT there. I have a hard time not spending money...