Metropoulos Forum

hey all! i am putting together an amp with an ultralinear/pentode switch and am still a little fuzzy on hooking up my ot to run in ultralinear.

i understand i put the ultralinear taps on the screens of the output tubes however i still have a 70v tap idk what to do with.

i did a search and i couldnt completely answer my own question. does any one have experience with the hammond 1645 ot or hooking up ultralinear/pentode switches?

thanks in advance!

-Brown Sugar

i apologize for such a noob question. i am starting out and trying to learn. gotta start somewhere.

man im an idiot. i figured it out. just dont know what the 70v tap on the secondary is for. help?

I'm not 100% sure, but if I remember correctly, 70V is used mostly for PA systems, like in a school etc, where it's a long way from the amp to each of the speakers in the individual classrooms. Each speaker had to have it's own transformer to step the 70v signal down to a usable amount.

But I could be wrong. It's been a while....

axeman wrote:

Is that for me, or OP?

Wattever wrote:I'm not 100% sure, but if I remember correctly, 70V is used mostly for PA systems, like in a school etc, where it's a long way from the amp to each of the speakers in the individual classrooms. Each speaker had to have it's own transformer to step the 70v signal down to a usable amount.

But I could be wrong. It's been a while....

No, you got it right. Here's a link w/ some info:

http://www.epanorama.net/documents/audio/70volt.html" onclick="window.open(this.href);return false;

For a guitar amp, you won't need to hook it up unless you're wiring it into a school speaker system ;^)

Just shrink wrap it and tie it off..

Dave

thanks elronhoover and wattever. i had read about 70v taps being for PA systems and running many speakers but i wasnt sure about this OT. i really appreciate the help guys!

-Brown Sugar

No problem, and don't worry about asking questions either, ask away IMO...

Dave

Well then I have another question

I'm trying to switch between Pentode and Ultralinear operation in a 4xEl84 amp. I know that the UL taps connect to the screens for UL mode and the OT primaries connect to the plate for Pentode mode. I have a DPDT switch but I'm having trouble figuring out how to switch between the 2 modes and how to wire the DPDT switch. Could someone please point me in the right direction? I keep researching it online however I haven't been able to find the information I need for this specifically. Thanks!

-Brown Sugar

Brown Sugar wrote:Well then I have another question

I'm trying to switch between Pentode and Ultralinear operation in a 4xEl84 amp. I know that the UL taps connect to the screens for UL mode and the OT primaries connect to the plate for Pentode mode. I have a DPDT switch but I'm having trouble figuring out how to switch between the 2 modes and how to wire the DPDT switch. Could someone please point me in the right direction? I keep researching it online however I haven't been able to find the information I need for this specifically. Thanks!

-Brown Sugar

Do you mean switch between pentode and triode operation?

Ultralinear is pentode operation; with UL, the screens are supplied by dedicated screen taps off the OT pri instead of a node off the B+ rail as in non-UL operation. Are you maybe trying to switch between UL and non-UL (both pentode) operation? If so, you need to figure how to simultaneously open the OT's UL screen taps and switch in the B+ rail screen supply node. BTW, that's not something you want to do when the B+ is up..

Dave

Yessir Im trying to switch between UL and non-UL. I also have a switch for pentode triode operation ill be putting in but that doesn't seem as daunting

-Brown Sugar

Hey, well you were 100% correct with your UL vs. pentode nomenclature, and I was wrong (i.e. UL is 'quasi-pentode' so to speak), so apologies for that..

A quick search and I only saw UL/pentode switching for single-ended amps, but if you dig around I'm sure you'll come up with it.

Dave