Choosing power tubes?

[Justin Thomas]

So, I did some voltage checks... couples minor issues. One, I'm gonna up my filter can to the 525V one, just for more wiggle room if testing w/out tubes is needed. The plates & screens are fine @ 430 & 395 respectively; I will prolly up them, since I'm using JJs. Why not? <BUT>, they are idling @ 21W, by my math... (!!! ) I'll fix it.

On another note, one side of the LTPI seems to not be conducting. Cathode of one section has ~50V, other side has nothing & full B+ on plate. I don't understand WHY, exactly, since they're connected right across the socket, so I'll be poring over that in the near future. Might explain the lack of gain, though!

Justin

PS: I swapped the preamp and PI tubes, same result. I highly doubt BOTH of them blew the same section! And, I just realized, I could have a heater wiring error, no?

PSS: resoldered the connections on the PI; voltages seem normal now. Going out to fire it up w. speaker & Teleblaster!

[Justin Thomas]

Another fire-spewing monster lives! I "radically" altered the preamp - EF86 into LTPI, feeding 2x6V6. Got an old Seimens 86 in it, and another & a Mullard & a JJ to try, too. So, it's still a Spitfire, but I think the original parallel-12AX7 just wasn't making enough drive to push the rest of the amp. It does now! I changed some other values to match my first build; I'll check back in with voltages later. Also need to tidy up the innards - the mods were tacked in. And still lower those 6V6s, idling @ ~20W/each! No explosions yet, though! And it's still near-dead-quiet with nothing plugged in, til all the knobs are cranked WAY up.

Justin

[The Dude]

Pictures please?

[Justin Thomas]

Still trying to graduate from Windows 2000 to Windows 10. I am taking camera pics, and when I figure out how to upload them, I will! And when it doesn't look like a grenade went off in a Radio Shack...

Justin

[Justin Thomas]

Got it "reasonably" operating... 465/455/38 on Plate/Screen/Cathode, respectively. Bias is a whopping 750R, for about 11.5W/tube. I may still up that, till it starts to sound bad... So, definitely use JJs! Cheap & expendable. I may pop in those RI TS5881s I have, or 6L6GCs, just to see... otherwise, sounds friggin awesome, and cleans up w. guitar volume. Does Crazy Horse easily, though not quite as farty. Liking this one, May be sorry to see it go. Still working on cleaning it up, but at least know how to post pics (sort of).

Justin

[Chuck H]

Liking this one, May be sorry to see it go.

I've felt that way with most of the amps I've made. But it's more gratifying to have your creations out in the world. Hopefully it's going to a good, local player that does gigs. Then you can go hear it in the mix used by someone that loves it. That's a good experience

[nosaj]

I've felt that way with most of the amps I've made. But it's more gratifying to have your creations out in the world. Hopefully it's going to a good, local player that does gigs. Then you can go hear it in the mix used by someone that loves it. That's a good experience

Yes there is no more of a compliment then to see someone coaxing magic from something you created from odd salvaged parts. The ones I build I plpay with them for a short bit then pass the amp around to people I know then I sell it after several opinions.

nosaj

[Justin Thomas]

I generally play mine out at least twice. If the original buyer doesn't want this one, I'll keep it. I need something between my Vibro-Champ & my Bassman... My Concert I still have to get from a friend. No worries, he's not trying to steal it or anything...

Justin

[Justin Thomas]

As promised, here's an attempt at pics... The 6V6 cathodes are grounded. The cap can is isolated from the chassis, and tied to the "sewer ground" with the PTCTs. Kinda ran out of room for the BFR, so the unconventional methods... I'll try & come up with a decent hand-drawn and error free schem. No trade secrets here!

[Chuck H]

My Concert I still have to get from a friend. No worries, he's not trying to steal it or anything...

Every time I loan out gear for an extended time it's always F#CK!NG TRASHED when I get it back. I would pressure those responsible for recompense, but they're musicians.

"Hey! A$$h0!es. When I said treat it like it's MINE I didn't mean treat it like it's NOT yours."

[Justin Thomas]

No, he's a good friend of 15 years, records "ragamuffin swing," plays weddings & high-falootin' parties with it. And a 67 Reverberocket, a 69 Dual Showman Reverb, a Gretsch Compact Recording, and a couple Booger-Ays for backup &/or Vocals. And he <KNOWS> how to treat that amp; he's nicer to it than me. Seriously, no worries here! Otherwise, if people wanna borrow my gear, they borrow me with it. And, most of my gear is already trashed, anyway! My Champ is proof...

Justin

[Justin Thomas]

After finalizing values and cleaning up a bit, I cranked it up some. There's a wicked crackle/loss of signal at high volumes, on sustained notes. The "Enzo Whack" says some chopsticking is in order... That, or a screen is about to go bye-bye! Will have to wait til next week, probably, and I guess I won't be taking it to my gig this weekend. Oh well, the Bassman behemoth still rocks!

Justin

[Leo_Gnardo]

There's a wicked crackle/loss of signal at high volumes, on sustained notes.

Sounds like bursts of ultrasonic oscillation. No scope? You'd see it immediately.

[Justin Thomas]

Nope, no scope. Got probes, but no scope...

I'll get it sorted out...

Justin

I blasted it again this afternoon, no problem... So the goal is consistency!

[Chuck H]

It seems silly to give greenhorn advice to you, but we do have our pat answers for trying to help so don't take it as an assumption of your skills. Ok?

If the amp is a combo, does it fail less or not at all if you plug it into a separate cabinet? If the amp is a head, does it fail less if you don't stack the head on the cab?

You actually already solved for this with the Enzo whack. If anything was revealed by hitting the amp, you know you have a bad connection or tube element. And you've already said as much. In this light I have to guess it's not an oscillation. But if there is any doubt then you need to pay attention to what sort of gain structure and/or controls exacerbate the problem in case it IS an oscillation.