Guild Masteramp (Tweed?) Schematic Help

[dorrisant]

Thanks for pointing the way!
I tried emailing Robert about info on his '55. Hope to hear from him.

Tony

[Default]

Thanks for pointing the way!
I tried emailing Robert about info on his '55. Hope to hear from him.

Tony

He seems to be pretty adept, technically speaking, although somebody should clue him into isolation transformers.

The $64 question is whether that dohicky is part of the tone circuit or a choke in the power supply. Guild did some pretty unusual things. For example, the transformer powering the heaters on the 12ax7s. Usually, those were run from the wall current like the rest of the tubes.
Almost all of the amps and schematics I've seen have had efforts made to control heater hum, certainly more than any company in the fifties and sixties.
Loud and clean seemed to be the watchword for each model of amp.

[dorrisant]

Got a reply... He is willing to help, but doesn't have a schematic either.

Looks like I just need to take the time to trace it. Hopefully I can draw it up well enough for some of the gurus here to break it down and help with a workaround if possible.

Tony

[Default]

Cool! I probably wouldn't get the mystery Guild amp from Florida until the middle of next week and I'm not even sure what it is.
Hopefully, I can get some time this weekend to go through the Masteramp here and draw a schematic and layout.

[dorrisant]

I stayed up pretty late last night tracing. More to do then I'll post a rough schematic.

Any suggestions on a good isolation tx for these amps?

Tony

[Default]

I am putting together a parts order and was going to call up AES and ask. I have another widowmaker on the pile and I need one for that too.

[Straight8]

Hey Tony, I went ahead and signed up so i could see what all the chatter was about regarding Masteramps.

Let me know if there are any specifics I can try to answer based on findings/comparisons in my amp. I'm pretty excited about the fact that you're tracing the circuit out. I tried doing that once many years back but kind of gave up once I had it all working again.

I've done some research in the past about isolation transformers and it seems there's a little more to it than just hooking up a tranny. (I've just been using mine 'carefully' in the mean time) I did a little googling earlier today and it seems the the Triad N-68X is a popular and inexpensive iso transformer for this application. The problem after that is the 35Z5 is a half wave rectifier. I'm not really an electronics guru, just a tinkerer, but it seems some additional rectifying will be needed so as not to damage the transformer. This amp is built a lot like old All American Five AC/DC radios. Radio forums seem to be providing good info that oddly enough relates to this amp.

All this talk has gotten me interested again in fixing a few leftover bugs in my amp and getting it back in tip top shape. It's amazingly loud for its size and really sounds great when cranked. It actually sounds better than the '57 version I have.

[dorrisant]

Welcome Robert, glad to have you in on this! I'm sure I will need some help from you.

I'm tracing right now... Hope to post a preliminary schematic soon.

Tony

[martin manning]

Maybe this is what is referred to above? http://www.instructables.com/id/Isolati ... /?ALLSTEPS
Triad N77U (100VA) might be big enough to handle the load without any other modifications, but at $42 (from Mouser) it is not cheap.

[dorrisant]

Let me preface this by saying that these drawings are rough. I know they are not efficiently drawn but they should get most of the circuit. I didn't completely draw out the power supply, leaving that for later. There are some ??? on them... feel free to help out.
I did see some evidence to indicate how the 'mystery coil' was likely connected - one end I'm sure of, the other not quite sure.
I have some breaks in the 'mystery coil' winding and need help with the value there as well.
I'm getting too tired tonight to continue tracing the power supply. Hopefully some of you may have seen something similar.
Also, for me the mica caps are hard to determine values for. My conversion chart doesn't show the configuration on these caps. I will post pictures later, but M1 at input jack 4 is a value by itself and the rest are all the same value. The ones of similar value all give roughly the same measurements on my crap meter, so i wasn't worried about their condition and I was going to leave them in. Stop me if I'm wrong.
On the layout, components in black are topside, components in red are on the bottom. The green is the wiring on both sides.
Anyway, I hope this helps!!!

Tony

[martin manning]

Looks like a fun little project you have going there. I haven't seen an inductor used in a termolo before. If it is damaged you will probably need to rewind it, which might not be too difficult. Maybe post a series of good detail photos so others can follow, say three across the chassis, front and back panels plus looking straight at the board, and a shot of the control panels from the outside. That would be good documentation for you to have too.

[Default]

Hi Robert! Glad to have you onboard! I don't think there's anything extra that you need to do to the circuit other than installing an isolation transformer. I could be wrong, but I've never heard of needing to add extra filtering for the transformer's sake. Over on the Guild forum, one of the brothers bought an early Guild that not only had an iso-tranny, but a choke added to the B+ to smooth out the ripple from the half-wave rectifier.

Going to print out the preliminary layout and schematic.
BTW, sign and date the layout and schematic, Tony. You need credit for doing this!

[Default]

On the schematic, the cathodes of the 50L6s are marked as [B+?].
The cathodes are most likely wired to a 2-5 watt resistor and possibly a bypass capacitor?

[Straight8]

Yes, the intrustables article was one I had seen as well as some info posted here ...

http://www.diyaudio.com/forums/tubes-va ... r-amp.html

[Default]

Yes, the intrustables article was one I had seen as well as some info posted here ...

http://www.diyaudio.com/forums/tubes-va ... r-amp.html

This is what he's talking about with the diodes rectifying the iso-tranny?

[img:609:211]http://www.jamesaudio.com/12vpowersupply.gif[/img]