Tino Z's 5b6 ptp

[RWood]

This is the pitts!!
I finished it last night, and did some final checking and testing.
I managed to get all NOS tubes from an electronics supply that's going out of business 50 miles away. They were all in original boxes...except one! Seems as though a rectifier tube was placed in one of the 6l6 boxes. I spot checked them but somehow missed that one. I called them today and they have no more 6l6 or 5881 tubes.
RATS!!! Now I'll have to wait a few days for Tube Depot to send some.

Randy's Law: If it can go wrong it already did, you just didn't notice it yet!!!!!

[RWood]

Got it together and found one of the new 6L6s was shorted.
I put a 5881 in its place for testing. After taking care of a screaming issue it settled down nicely.
This amp is so quiet its hard to believe it has all these long leads!
There is only the slightest oscillation with my bass but I kind of dig it for now. The .1 snubber cap killed a lot of headroom for some reason so I took it off till I can study it some more.
Octal tone for bass is definately where it's at!!!!

I have a 15' Weber bass speaker going in an EV TL-606 tuned cab I just finished. Will post pics after I get it covered in a day or so.
The amp will be going in a matching head cabinet.

[David Root]

I've been seduced by all this loose talk about how great the 5B6 circuit sounds and plays, so I'm going to bite. Haven't done a tweed since my corksniffer's 5E8, which worked out real well, and I've never done an all-octal tweed.

Right now I'm rearranging the Fender layout so it's more like a "normal" Fender layout, ie NOT with the pre and PI in between the rectifier and the power tubes, but in line from pre to rectifier.

I'll use a board with the same basic layout, Leo prototyped it for me so why reinvent the wheel? I just don't like all that flying wiring with the pre and PI in the middle. I guess it was done that way to get the 15" speaker to fit between the PT and OT, but I'm doing a head because of the documented microphonicity of the 6SC7, so that does not apply.

I do have a couple of questions of those who already built the 5B6.

1) PS cap values. I've seen many say 4x16uF is a bit too saggy when cranked, so what values are "just right" for modern playing? The 5U4G drops a lot of voltage so I would think it wouldn't sag too much. I know two in parallel (5E8) are pretty tight for a tweed.

2) How about an extra 8uF just for the 6SC7? I look at one 16uF cap for four triodes and hear putt-putt-putt.
I have been thinking about 40/600 for the plates, 20/600 for the screens, 16/500 for the PI and 8/450 for the 6SC7. That's 30% more than the original. Is that too much?

3) Anyone try a small choke instead of the 10K resistor? How does it sound? does it change the 5B6-iness too much? If not, I could use a 5R4G with the choke instead of a 5U4G with resistor, the 5R4G drops a bit more voltage than the 5U4G. (5R4G is just a high voltage 5U4G I'm told). I use 5R4Gs in my 5E8, because they sound much better than the 5U4G, no idea why, but it's real and not subtle either.

[martin manning]

Re the PS filters, I've read that most of the older electrolytics were well over the marked value, by as much as 50%. Given that, maybe sub 22uF for 16uF?

[M Fowler]

Nice job on your build.

I didn't use that .1 snubber cap and when I tried it the amp didn't work well.

In Tino's instructions he said it is an option if there is super sonic oscillation at the 6L6 P/P stage shown by the amp breaking up and not controlled by volume Fender used a 0.1uf cap to stop this.

Tino spec'd for his design a 3 section cap cap 30/20/20 and I used can cap 40/20/20.

[David Root]

Thanx guys. So 40/20/16/8 isn't out of line then.

Here's my "rearranged" ie cut n' paste layout, very rough and subject to some tarting up to make it look semi-respectable, not to say legible.

I'm thinking of using an old BF Vibrolux PT, which has enough 6.3V current rating that I can try out a pair of KT66 in it, as well as 5881 and 6L6GC. Would I be pushing my luck on the HT current with a pair of KT88? Just curious, with cathode bias I don't think so, HT current was about 180 - 200mA rated on the BF Vibrolux PT I think.

I have a '68 Bassman OT that is looking mighty tempting here too.

[RWood]

I used 500v 47/22/22 because I had them.
To me it sounds great.
I'll probably try a choke just 'cause I'm a curious type. If I don't like it I'll yank it out.
I wish I'd had one of these 30 years ago!

[David Root]

RWood, what OT did you use? What is the Zpri?

[RWood]

I used Weber W022848 40w 4k primary, 4ohm secondary OT.
Weber W022798 40w 720v/660v PT
Here's the new house I built for her (Peggy Sue)
Front panel removable for easy access to tubes

[David Root]

After reading some of the earlier posts in depth I was about to change my mind and go to PTP. Then I saw ToneMerc's post and that seems to work fine so I will use the board.

No-one seems to know what the 5B6 PT HT voltage was, but I put it into PSUD2 at 325-0-325 and it came out very close to Tino Zottola's voltage on B+1, so I'm going to run with this old Vibrolux PT I have.

Can't afford (or find) a Triad 2820 OT so I'll not use a '68 BF Bassman I have as that's probably overkill for a 30W amp. Will have to find a good 35-40W OT.

[RWood]

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

[tictac]

I also bit the bait on the 5B6; made a little head with the voltages results very close to the Tino schematic...

Little bugger make a JBL D-130 sound sweet; maybe why steel players seem to like this circuit....

TT

[ToneMerc]

After reading some of the earlier posts in depth I was about to change my mind and go to PTP. Then I saw ToneMerc's post and that seems to work fine so I will use the board.

David, yes that 5B6 eyelet board layout I used works great. Come to find out that the distortion artifact I was chasing was not the amp at all. It seems my 140W 700V high plate ODS killed that test speaker. Maybe one day I will build another in a config with 490-500V and KT88's.

TM

[RWood]

Looks like I owe Tino an apology for misspelling his last name so many times. I wrote it down wrong on my bench the first time I saw it.
Sorry Mr. Zottola

[wyatt]

So, since this is an active conversation...

How many are using the (relative hard to find) 6SC7 for V1 and how many are rewiring to use a 6SL7 in that spot? Is there a major difference.

I know the difference in the construction between the two, but I always assumed the performance of the triodes were pretty similar.