Tino Z's 5b6 ptp

[M Fowler]

I use the 6SC7 tube V1 and 6SL7 V2.

I recently changed my 50w Bassman iron 5b6 to Ampeg B15N circuit with all 6SL7 preamp tubes. LTPI and running 6550's.

Currently building another 5b6 cage amp keeping it Tino simple PTP but using axial filter caps not can caps. Will use 6l6GC's on this amp.

[RWood]

I found nos RCA "Meatball" 6sc7 locally, but I also ordered new Russian Sovtek from Parts-Express for spare, so they must not be that hard to find.

[David Root]

ToneMerc, I looked over your post again in detail, and decided to get the same iron you used ie the Valco/Supro Thunderbolt pair from Mag Cpts. So I probably won't be able to run KT66s in it, but a nice pair of RCA blackplates or NOS Tung-Sol 5881s should both sound good in it.

I put the Valco PT into PSUD2 and it gives 429V B+ with the 5U4G, but 408V with the 5R4G, which is fine with me, I like the 5R4G a lot in my 5E8A. 5AR4 comes in at 460V, a bit high (but might work OK with KT66s??).

I just didn't feel like hacking the PT cutout in the chassis, even though it's aluminum and only 3/32 thick.

I'll be using .05 red Jupiter caps, I actually had four in stock, back from my 5E8 when I couldn't decide to use .1 or .05. See pic below. I got all the CC resistors from Parts Connexion. Somehow I forgot to get a 27R, will have to see if I have a couple 47R I can put in parallel.

The little bypass cap in the 6SC7 spot is a Black Gate 220uF 4V that P-C had for $0.95 each, cheapest B-G caps I ever bought! Just to see what it sounds like, for a buck, why not?

I put a 100V cap on the power tubes' cathode, since I'm told 50V is a bit low maybe at startup. Nichicon Muse 22uF.

wyatt, I got four Tung-Sol 6SC7GT on fleabay for $56, not too bad. If you look at the 6SC7 plate curves they are very nicely spaced which means a very linear tube. I think the 6SL7 is very similar, judging by its plate curve. some say they do sound a bit different, we shall see.

[jon]

Well this one's in the books finally with the completion of tuned cab built to EV TL-606 specs with 15"Weber bass speaker.
I may revisit this build with tolex cover someday, but not for now.

Amp head with removable front for easy access to tubes, vented screens front and back to keep tubes cool.

I built it for miking bass through board, but will likely do a line out mod also.

It ended up being the quietest amp I've built yet. PTP is the way to go with these.

100% creds to Tino's build layouts

How do you like the weber in the tl cabinet. I've used all sorts of drivers in mine and I currently have a k140 in it. While not the same I really liked my supro thunderbolt through my tl, real woody tone.

[RWood]

Jon: The plans call for 3" fiberglass insulation inside but I used 2" egg crate type foam. The first speaker I tried was Fender branded(looks Jensen made) which was a bit looser on the bottom than the Weber 175W bass speaker, which has super tight bottom end with this cab with no echoy resonance, just pure bass punch. I liked it better without the stepdown panel. Of course it's not broken in yet so I can only assume that it will get even better.

BTW I plugged my 5F1 champ with 5881 tube into it and played Les Paul on brite bridge pup and WOW!!!

This is by far the best bass speaker/cab combo I've heard and it makes the 5B6 sound much bigger. I highly Recommend The Weber.

Complete builders' plans are available on the net, just google EV TL-606 plans

[David Root]

Here it is finally, just finished, Son-of -Tonemerc's board & layout, but in a longer chassis (which may or may not be a good thing, we shall see). It's a tubes-up layout with Fender-style faceplate ie inputs on left, power on right.

I have been delayed some lately as we have recently sold our house and bought another smaller one 40 miles further out from Vancouver. Mucho paperwork, inspections, bank, mover etc. etc. With any luck this will be my last move, I'm retiring from my day job at the end of June.

Then I'll have more time to build more amps!!

I put in 33K grid resistors on V1, but none on the power tube grids. If it misbehaves when I crank it I'll put in a pair of 1K5s. I did put in screen resistors, as you can see. I hope that Tung-Sol 6SC7 is not microphonic, but I have three backups so I should get one good one.

[M Fowler]

Looks great David. The only reason I like small chassis is so I can wire it PTP.

[ToneMerc]

Here it is finally, just finished, Son-of -Tonemerc's board & layout, but in a longer chassis (which may or may not be a good thing, we shall see). It's a tubes-up layout with Fender-style faceplate ie inputs on left, power on right.


I put in 33K grid resistors on V1, but none on the power tube grids. If it misbehaves when I crank it I'll put in a pair of 1K5s. I did put in screen resistors, as you can see. I hope that Tung-Sol 6SC7 is not microphonic, but I have three backups so I should get one good one.

Looks great David, looking forward to see what you think of it.

Mike

[David Root]

Thanx guys!

One thing I'll be watching is the signal line from the volume pot wiper to the phase inverter grid.
It is pretty long as it goes from the pot on the front of the chassis thru the send & return jacks on the back of the chassis and then out to the PI grid, pin 4.

[Blackburn]

Great looking build! I really dig this circuit and want to do another one this year at some point. That rectifier is badass!

[David Root]

Thanx B! That rectifier is a 5R4GY, 1950. Cost me $50, you could get them 2 or 3 years ago for half that. Hifi guys discovered them unfotunately. I have two 5R4Gs in my '57 Twin build, sounds awesome.

[David Root]

Been busy this week, just tried her out this morning on an Avatar open back cab with an old Altec 417B, original cone. Parts Tele with Voodoo Pickups '62 model.

Sounds very good indeed. Changing the four .1uF coupling caps to .05 and leaving the high value cathode bypass cap on the 6SC7 (220uF) seems to balance very well with the Tele. Haven't tried ny 335 yet.

I started out with the 5R4GY in the pic, not a 5U4G, and the voltage is OK so I haven't even tried a 5U4G as it would probably be a bit too much B+ compared to the 5R4GY.

No hum or noise, even with the long unshielded run from the volume pot wiper to pin 4 of the PI. Cranked right up, there is a little high end hash, sounds like an oscillation, I'll have to chopstick that.

Heater voltage is 6.5, that's OK. I too had to change out the 270K plate on the 6SC7 to 180K. My 180K measures 200K, a bit out of spec. Now get 162V on the plates and it definitely makes a headroom and volume difference.

All in all sounds like an OK build. I recommend it if you have a "need for tweed".

Didn't have to roll any tubes and the 6SC7 is not microphonic at all. Hopefully that won't change as it gets played in.

All other voltages very similar to Tonemerc's values. 27.3V on the 5881 cathode bias.

[ToneMerc]

Been busy this week, just tried her out this morning on an Avatar open back cab with an old Altec 417B, original cone. Parts Tele with Voodoo Pickups '62 model.

Sounds very good indeed. Changing the four .1uF coupling caps to .05 and leaving the high value cathode bypass cap on the 6SC7 (220uF) seems to balance very well with the Tele. Haven't tried ny 335 yet.

I started out with the 5R4GY in the pic, not a 5U4G, and the voltage is OK so I haven't even tried a 5U4G as it would probably be a bit too much B+ compared to the 5R4GY.

No hum or noise, even with the long unshielded run from the volume pot wiper to pin 4 of the PI. Cranked right up, there is a little high end hash, sounds like an oscillation, I'll have to chopstick that.

Heater voltage is 6.5, that's OK. I too had to change out the 270K plate on the 6SC7 to 180K. My 180K measures 200K, a bit out of spec. Now get 162V on the plates and it definitely makes a headroom and volume difference.

All in all sounds like an OK build. I recommend it if you have a "need for tweed".

Didn't have to roll any tubes and the 6SC7 is not microphonic at all. Hopefully that won't change as it gets played in.

All other voltages very similar to Tonemerc's values. 27.3V on the 5881 cathode bias.

Good deal, glad that layout worked out for you as well.

TM

[RWood]

Very tidy build David. Congrats.

I can't seem to describe what I like so much about these octals. A little raw but still refined... Edgy and clean at the same time...Top end as delicate as the bottom is strong?

I'd like to hear how others describe them.

Equally as good with guitar as with bass, so it is really hard to classify. I wish I still knew a harp player to hear through it.

[armillary]

Not a 5b6, but I have a 6SC7 in the Princeton 5C2 clone I'm working on. It uses one stage of the 6SC7 to drive the other, like Fender's later 12AX7 preamps did. It has a plate voltages around 160 and a strong overdrive. The going rate for 40's or 50's era NOS 6SC7s is about $10 or $15. They're not noticeably microphonic in operation, but if you tap the shell with your fingernail, they respond with a "ping" that sounds like sonar from the movies.