Ampeg B-15N Schematics

[txstrat]

No, I used an ultralinear PT from a supplier 'round here. But I didn't use the OT taps for the screens.
edit: I think you could use a 125A30A OT.

[dpacek]

Thanks much thats a big help.
Back to the added 6L6GCs.... do I need to add additional resistors or caps anywhere ?
I'm looking at the same schematic you started from (Joe Piazza B-15-N 1968)
thanks for your patience .. i only know enough to be dangerous sometimes ..
I will get my own copies of the TUT 2 and 3
soon.
Dan

[txstrat]

Back to the added 6L6GCs.... do I need to add additional resistors or caps anywhere ?

Just the additional resistors to the added power tubes screen and control grids. Bias properly.

I will get my own copies of the TUT 2 and 3
soon

The B-15 project is in TUT 3 (including layout) but it's not the version I built my amp from (different schematic).

[dpacek]

Just the additional resistors to the added power tubes screen and control grids. Bias properly.

The B-15 project is in TUT 3 (including layout) but it's not the version I built my amp from (different schematic).

I see Hammond makes the 1650R - I'm thinking that should be good enough
to handle the output from the 4 6L6GC s

or should I go bigger like the 1650T ?

[loudthud]

The 1650R is really intended for a B+ of 600V or higher. Ideal for amps like what are being talked about in the Dual Rail thread: http://music-electronics-forum.com/t19103/ Those amps use a single pair of 6550s or KT88s. The 1650T is better suited for a quad of 6L6GCs with a B+ around 500V. IMHO That will give you more of the B15 flavor than the higher voltage setup, but I have yet to play an amp like that with a soft power supply.

[dpacek]

Thanks, thats a huge help. I'm still a little confused as to why the Hammond spec sheet at Hammond Mfg. - "Classic" Push-Pull - Tube Output Transformers - (1608 - 1620, 1645 & 1650 Series)
says that you can use a 1650N OT with 4 6L6GCs (parrellel pairs) and only get 60Watts out.
I was thinking that adding the 2 6L6GCs to the B15 power amp circuit would put me closer to 85-100Watts
apparently I'm not taking all the variables into account here.

But then again i think my hopes of creating a 100W version of B15 may be
beyond what can be accomplished with this circuit without sacrificing tone.

[txstrat]

Don't worry, I built one with a 50-60W OT and two 6L6 and I assume it's got no more than 45W. But it's plenty against our (loud) drummer. (BTW 2x10 Beringer cab)
If you build it with four 6L6 you get some more watts to your advantage. For a bigger venue you can easily add a line out and send it over a PA-system. That's what I did. Sounds great over the PA speakers also.

[dpacek]

So you think the 60W Hammond 1650P will be heavy duty enough to handle 4 6L6s ?

[txstrat]

So you think the 60W Hammond 1650P will be heavy duty enough to handle 4 6L6s ?

No, that's not what I'm saying.
MY OT is made of iron enough for 50-60w at around 500v for two 6L6 and runs at 420v. That's why I assume less output.
If you want to use four 6L6 you ought to use an OT for four 6L6 and a max of 500v. An OT intended for a B+ of 600v or more might not run at it's best at 500v. Four 6L6 have a different plate to plate resistance than two. That's why (among others) you need a different OT too, not to stress the tubes and the OT.
What loudthud proposed you should go for an OT which is intended for a B+ of 500v (and four 6L6).

[dpacek]

Thanks I follow you now. So the 1650T is the best bet if I want to go with 4-6L6s .
The PT used in the TUT3 Portaflex design is the Hammond 270FX which yields 370Vdc, should I go bigger ?
thanks again for your patience, I have my TUT1 and TUT2 books on order as well so I can start
asking smarter questions.

[txstrat]

Generally spoken less voltage means less high end. Although it is a bass amp it needs high end too. I went for 420vdc. But that's just me. It'll work with 370vdc as well. Don't know what the genuine voltages were.

[dpacek]

So when you built your B-15N from the 1968 schematic and went to 4 6L6s which PT did
you use ? How much power (watts) do you think you are getting ?

[dpacek]

The 1650R is really intended for a B+ of 600V or higher. Ideal for amps like what are being talked about in the Dual Rail thread: http://music-electronics-forum.com/t19103/ Those amps use a single pair of 6550s or KT88s. The 1650T is better suited for a quad of 6L6GCs with a B+ around 500V. IMHO That will give you more of the B15 flavor than the higher voltage setup, but I have yet to play an amp like that with a soft power supply.

Thanks ... I can't seem to figure out from the Hammond site which PT I should use to power the B15 circuit with 4 6L6s with a 1650T OT .. KOC claims the Hammond 270FX in the circuit will only yield 370VDC . What are the specs I should be looking for to get to 500 V ?

[txstrat]

So when you built your B-15N from the 1968 schematic and went to 4 6L6s which PT did
you use ? How much power (watts) do you think you are getting ?

I had the PT wound by a local supplier. It's got 300vac secondaries @ 550mA (400mA would have been plenty). I ended up with 423vdc and biased the amp at 48mA which should give a plate dissipation of around 20w per tube/ 80w altogether. I think the calculation of wattage isn't the most important factor. I simplify my thoughts by speaking about two or four power tubes with a matching OT. Two are enough for every club... four are plenty. Well at least with a guitar amp. For a bass amp I think four tubes are enough for every club. (think of an efficient cab too).
If you want the amp to be louder, twice the speaker surface would give you more headroom than a bigger power amp. Well, at least to a degree.

[dpacek]

I can see why you went to a custom PT, I can't find anything from hammond that delivers that kind of current (400mA)
with out going over 500vac secondaries (Hammond Mfg. - Universal Primary - "Classic" Power Transformers).
not sure what to do next except look for my a custom winder myself.

Perhaps I should stick to the 2 tube configuration and use a larger PT and OT ?

The B-15R (reissue) from Ampeg had a 60/100 watt configuration
I wish I could find the schematic for that.


with regards to speaker surface, I'm thinking of something in a 4X10 configuration.