PT with no HT center tap

[Baxtercat]

Hello guys [and gals],
I finally started my next amp project w/ these two trannies [maybe from a Leslie? I've forgotten].
I just noticed there's no orange/yellow CT tap to ground from the PT.

Dang, I can't just follow my old Fender-type wiring scheme this time.
What do you do in these cases?

Here's a pic. of the PT wires:
2 black; 2 green, 2 yellow [5v?], 2 red, and 1 6.3 CT
[the black on the right is to the choke]



Thanks in advance.

[txstrat]

Are you aiming for a diode or tube recto?
With a diode bridge rectifier you don't need a HT center tap.

[Baxtercat]

That's it...
I forgot. I must've skimmed over those pgs.

I've got a nice little bridge assembly in my cigar box of parts somewhere.
I'll be back w/ pics when this gets close to done. Hopefully I won't be back w/ too many questions. [You probably see the same ones over and over.]

Thank you txstrat.

[txstrat]

Hopefully I won't be back w/ too many questions. [You probably see the same ones over and over.]

That's what this forum is for. (maybe not to be repeated over and over but to answer those questions)

[Baxtercat]

Well, I got this scavenged pile put together and have been gigging it out all weekend.

Figuring it out has been a pretty roundabout process but I used a bridge recto for a while, then realized I could [should!] do better than 200+ volts. I webbed around till I found info for making a voltage doubler, got it up to 440V.

I didn't have a winding for fixed bias and was worried about the 6P3S's so I hooked it up K bias [now about 370-375 between K and the plates].

A friend found me four anodized TV legs...which called for this 'Marvin the Martian' motif. I made a box from leftover shelves, Mod-Podged some Tiki textile around it, and added an old 12-inch EV Force speaker. [I think all I spent was $10 for the handle, $7 for the white piping, and $6 for fabric.]

The chassis originally ran two 6973's plus a bunch of other tubes. Even with the four Sovtek wannabe '6L6's now, the amp only sounds like 30 watts. I guess the limitation is the OT in that case. Nothing is running hot though. In fact the tone is great.

The large radio knobs spin but that's about it. The real controls are accessed from the back, where I wired up a preamp, pilot light, on/off switch, input jack, and so forth.

[txstrat]

I'm impressed. Looks great.

[Enzo]

I love the grille cloth.

[gsr]

I love it! Very creative.

[Chuck H]

+++
Not one detail looks fudged. It's like a perfect "Jetsons" cartoon amp. Love, love, love it.

Chuck

[Baxtercat]

Thanks all, I appreciate it.
It's been a hit amongst our fans [err, barflies, Hah!]
Some think I used an old TV set [as if!]
Here's another angle, and also a shot showing my barbarous layout and soldering...



Neat looking potted tranny. I'm still not sure I used it right.

[txstrat]

The first pic looks like Marty McFly of 1955 would jump right out of the picture. Great. Got some sound clips?

[loudthud]

I don't think too many people will want to set their beer on that amp!

[Baxtercat]

Hey, maybe the anti-drink-skid feature will help me cut back on ales.


Clips? I don't know how to do that, but I usually twist the knobs on every rig until it sounds the same—kinda Fendery.

Hate to kill the thread but here's a recent instro through another homebuilt amp: [I'm on the right]

[tubeswell]

That's one helluva cool amp Bob. I like that anti-beer-can feature - In the original shot I was fooled by the camera perspective into thinking it was a square box - nice one. You've inspired me to make my next cab with ABC.

[Chuck H]

That's a really great tone. Are you using a compressor? There's some nice sustain and a soft attack but no muted treble and it rings real clear. I like your tone better than the guy on the left (but don't tell him I said so )

Chuck

[Baxtercat]

...too late [I told the sit-in guy anyway, a few weeks ago] :-D

Yes, I use an old DOD comp. for my boost and tend to run cleaner than some. [that grit was great in the late '60s and '70s but I get tired of hearing it all the time]

Technically minded readers....I bought a purple/blue 6-LED 12V assembly to light up the inside of this combo. I thought just a little cap and recto off the 6.3V would be enough [gives me under 9 volts DC] but the 6 diodes don't light up [they do with a 12V wallwart but I have no room in back for that].

Is there a way to bump up that DC another volt or two?

[Chuck H]

How about a voltage doubler rectifier and regulate back down with a zener. Plenty of current at the wind to support it.

Chuck

[Baxtercat]

I finally got the LEDs goin' in the Jetson TV amp. I found a cheap little chrome bezel w/ 6 UV-colored LEDs in front. That'll finish it off, at least until I find a Philco or some other TV badge.


I bought a similar fixture for inside, a 7-inch bar w/ about 8 blue LEDs. There's really nothing worth lighting up back there, but what the heck. They're a lot brighter and nearly wash out the orange pilot light.
I like 'em. I'll probably get some more blue ones if/when the purple front ones burn out.


To power these I found a small 11+ volt wallwart and installed it under the chassis to an RCA jack, to plug in the light leads.
I didn't know enough to figure out an 11v DC scheme with a Zener diode and a little voltage doubler off the 6.3V. Next time though.

Now I know why the thing sounded like 35 watts. I had too large a cathode resistor to the power tubes. They were only running around 18 ma each. I found a 250 ohm/12 watt and swapped out the 650 ohm. Now I'm getting from 32 to 39 ma.
That sounds hotter than I run a Fender; you think that'll be OK in a K-bias amp though?

[JHow]

Awesome amp! This is just the kind of creativity I would expect from a denizen of Pacific Grove! Nice job!

[Baxtercat]

Denizen! ...good word. Like skulker, lurker, cave dweller. All apt for Summer here today: it's downright cold and damp. Might as well stay in and tinker.

[txstrat]

Now I'm getting from 32 to 39 ma.
That sounds hotter than I run a Fender; you think that'll be OK in a K-bias amp though?

I think 32 to 39 ma is not to hot for k-bias. 250 ohms is the value most k-biased Fenders with two 6L6 ran at, anyway. Do the tubes redplate?

[JHow]

..Summer here today: it's downright cold and damp...

I feel your pain. Some of my mis-spent youth was mis-spent at the Presidio. P.G. always impressed me as being kind of quirky and artsy (I mean this in a good way). I was really into rock-climbing in those days and we used to go "bouldering" on the sea-wall at the local park. There were often a bunch of SCA guys in the park wearing armor and whacking each other with rattan "swords". It had a fun vibe.

[Baxtercat]

Hiya Tx...[just saw your reply here; thanks]
No, the 6P3S's seem to be running fine. The amp is nice and loud too.

It's still a tad 'bluesier' than the Twins or Bassman amps I'm used to.
So, next I'll try:
a) deleting some midrange with a cap and resistor,
b) a slightly larger K resistor, and/or
c) fixed bias, once I figure out where to get some voltage for that.

[Or leave it softer—some folks pay for that feature.
Heck, I've got plenty of amps.]

[Baxtercat]

I added a plexiglas porthole to beam more sterilizing blue light rays out.


...and my daughter just made a 'video' from an old TEAC deck original instrumental I'd recorded about 23 years ago.
She shot the footage around the neighborhood [and in the house] and put it all up on YouTube.

[Reef Walker]
YouTube - Reef Walker (Original Instrumental)