|
Post by Mike the marksman on Mar 23, 2021 8:11:53 GMT -5
And he wants me to build it. I'm somewhat experienced in electronics assembly, have an associates degree in electronic technology and am solder certified, but I've never built a tube amp before. I tried to convince him to start with something smaller (6G3 brown deluxe or 18W Marshall) but he wanted the twin. He's not too concerned about it being built quickly and it was mostly a "just for the hell of it" purchase.
Any tips for a first timer?
|
|
|
Post by Leftee on Mar 23, 2021 8:21:47 GMT -5
|
|
|
Post by Auf Kiltre on Mar 23, 2021 9:56:37 GMT -5
Does your buddy have small children? Make sure to buy them the most convoluted assembly-required toys for their birthdays, lol.
|
|
|
Post by Mike the marksman on Mar 23, 2021 10:04:54 GMT -5
No, he doesn't have kids, lol. He's a single 27 year old with alot of disposable income.
He didn't explicitly say he wants me to build it, but I've seen his soldering skills (he has none), so it's just kinda gone unsaid that I'll be doing most of the building, or at least looking over his shoulder instructing him. Why he chose a HP tweed twin I don't know, seems like an odd choice.
|
|
|
Post by Auf Kiltre on Mar 23, 2021 11:23:53 GMT -5
Unbridled ambition. Kinda like choosing stainless steel frets for my first stab at a refret.
|
|
|
Post by Leftee on Mar 23, 2021 11:35:08 GMT -5
He really should have started with a Tweed Champ.
There is nothing worse, in amp-world, than trying to straighten out someone else’s misbuilt mess. Especially if they lack decent soldering skills.
|
|
|
Post by Mike the marksman on Mar 23, 2021 12:55:26 GMT -5
I do have access to a variac, and I could rig up a current limiter. Just an incandescent light bulb in series with the AC cord, right?
|
|
|
Post by Leftee on Mar 23, 2021 13:01:11 GMT -5
|
|
|
Post by Leftee on Mar 23, 2021 13:05:56 GMT -5
I should build one and take some excitement out of my life.
|
|
|
Post by Pinetree on Mar 23, 2021 14:11:27 GMT -5
Build an Allen iff'n yer gonna build one.
|
|
|
Post by Mike the marksman on Mar 23, 2021 14:21:25 GMT -5
He already bought it, and I don't think Allen makes a 5F8-A kit.
I'm not terribly keen on Tweed amps, personally. I would be more excited if he wanted a plexi Marshall circuit, Vox AC or a brownface Fender.
|
|
|
Post by Mike the marksman on Apr 26, 2021 10:16:49 GMT -5
Kit was finally delivered and we started on it yesterday. Tube sockets, pots, switches, transformers, choke, jacks and speaker outs are installed. Board is populated, but not yet soldered. Will cut and solder flying leads this evening.
The kit came with a schematic and wiring diagram, but no other instructions or documentation. Had to do some digging online and print some visual aids and more detailed diagrams.
|
|
|
Post by Leftee on Apr 26, 2021 10:18:19 GMT -5
😎😎
Post pics if you can. That’s good stuff.
|
|
|
Post by Mike the marksman on Apr 26, 2021 14:11:37 GMT -5
We're taking pictures as we go, as soon as I can figure out some photo hosting I'll post them:)
|
|
|
Post by Leftee on Apr 26, 2021 14:22:00 GMT -5
😎😎
|
|
|
Post by LTB on Apr 26, 2021 21:16:26 GMT -5
I made one 16 years ago. I used a clip in cylindrical Halagen bulb so I could get up to 5 amps to the amp being tested without significant loss in voltage. My brainiac idea nearly blinded me ( LOL ) so I had to put a piece of 1/4" thick dark glass in front of it
|
|
|
Post by Mike the marksman on Apr 29, 2021 7:03:05 GMT -5
It just occured to me that this thread is probably in the wrong spot, if a mod could move it to the Amplifier Workshop..
So I have the PT completely wired except for the 50V bias supply, which is hanging loose for now. I plugged in and powered on for the first time yesterday. I'm getting 330VAC off each side of the the HV secondary to CT, 7VAC across the 6.3V filament winding (approx 3.6VAC from each side to the center tap), 49.5VAC off the bias supply winding. I plugged in a rectifier tube and I'm getting 455VDC off the standby switch, unloaded and not yet wired to filter caps.
The turret board and cap board are populated, under-board jumpers and most of the flying leads soldered in place, and the filaments are wired on the octal and 9-pin sockets. I still need to drill holes in the chassis to mount both boards.
|
|
|
Post by Pinetree on Apr 29, 2021 14:21:07 GMT -5
Need moar photos!
|
|
|
Post by LTB on Apr 30, 2021 0:56:33 GMT -5
He really should have started with a Tweed Champ. There is nothing worse, in amp-world, than trying to straighten out someone else’s misbuilt mess. Especially if they lack decent soldering skills. Especially if it utilizes point to point wiring. How you run the wires can effect its operation by inducing noise and oscillation
|
|
|
Post by Mike the marksman on May 6, 2021 7:10:05 GMT -5
Well, there's a problem. I think I have a short somewhere. Powered the amp on with a light bulb current limiter. The fuse held and the caps didn't blow, but after about 7 or 8 seconds of flipping the standby switch I started getting a very loud low-frequency oscillation through the speakers, with all the knobs on 0. It was loud enough to make me jump and I immediately unplugged the amp. Pulled the preamp tubes, turned the amp back on and got the same oscillation, just not nearly as loud. The pilot light and the light bulb current limiter are flickering at the same frequency as the oscillation, which is steady, and about the same speed as a drum roll, or a machine gun. Pulled all tubes but the rectifier and plate voltage is not dropping after the power tubes like it should, pin 1 of V1 is reading around 450VDC(!). I measured resistance across the 4.7K and 10K dropping resistors and they measure like they should. I was bummed and decided to call it a night. I'll leave all the tubes out but the rectifier and check all voltages when I get home later.
Oh boy:(
|
|
pdf64
Wholenote
Posts: 558
|
Post by pdf64 on May 6, 2021 19:36:19 GMT -5
|
|
|
Post by Mike the marksman on May 7, 2021 7:19:10 GMT -5
Update; It works! kinda.. I rewired the filter cap board according to Rob Robinette's 5F6-A layout instead of Mojo's layout, and the motorboating is gone. I also found that I accidently put a 1M resistor on the grids of two of the power tube sockets, when it should have been a 1.5K, so I replaced it with the correct value resistor. I did have the correct value on the other two sockets.
I can now play through the amp, but the normal channel volume pot doesn't work- it passes signal and is fixed at fairly low volume. The bright channel volume pot does adjust volume, but still passes signal at 0. The prescence, bass, middle, and treble pots work as they should. I'm also getting quite a bit of 60-cycle hum, but I think I just need to do some chopsticking for that. I'll doublecheck the voltages, hopefully figure out the volume pot issue, and check bias later this afternoon.
Aside from the volume pot issue and the hum, I'm pretty impressed with how the amp sounds.
|
|
|
Post by Mike the marksman on May 12, 2021 7:10:39 GMT -5
Pictures are forthcoming, but after fixing a couple small issues the amp is done. It sounds great, is hum free, and we're both really happy with it. Hooked it up to an attenuator last night and put both channel volumes on 12. It rips! I'm glad I was able, with my limited experience and with some forum help, to figure out the bugs and get it up and running without having to take it to an amp tech.
|
|