Isolation transformer with point to point amp.

[Steve_P]

I'm working on one of these and I understand that you have to use an oversize isolation transformer for a single ended amp to avoid saturation. In this case, The preamp has it's own filament transformer, and the power tubes are push-pull, so I'm only have to be concerned with the B+ the heaters for 2x50L6GTs and a 35Z5GT. The other side of the rectification is provided by a couple of solid state rectifiers. The power tubes are pulling 100 milliamps for the two of them. It seems to me that, including the heaters, that I shouldn't need much in the way of a transformer to make this safe, but I am not sure what the requirements are if core saturation isn't an issue. Thoughts?

[sluckey]

Schematic?

[Steve_P]

In the process of drawing one. One leg of the B+ goes through the 35Z5 and the other goes through silicon voltage doubler. About 185-190 on the plates. 2x12ax7s preamp and phase inverter, 6SN7gt for trem. Simple cathode bias amp.

[Steve_P]

Voltage on the screens is high (165), so I have to muck with the power supply a bit.

[sluckey]

Who makes the amp? Can you post some pics? 2x50L6 plus 35Z5 = 135VAC for heaters. Are these wired in selies and connected across the 120VAC line?

[Steve_P]

Who makes the amp? Can you post some pics? 2x50L6 plus 35Z5 = 135VAC for heaters. Are these wired in series and connected across the 120VAC line?

It's a 1955 Guild. There are no official schematics for these. I found a partial schematic over at the Ampgarage, and had a partial schematic in an amp I have. A lot of differences between these two obstensively similar amps. Saw this in the other thread.

Set your meter to measure AC current. Connect the probes across the fuse holder lugs. Pull the fuse. Turn the power on and measure the current draw.

[Steve_P]

Who makes the amp? Can you post some pics? 2x50L6 plus 35Z5 = 135VAC for heaters. Are these wired in series and connected across the 120VAC line?

According to one partial schematic, (and it's the case in the one I'm working on), the heater string for the rectifier and power tubes drops to neutral/chassis ground via the the power tubes'  150 ohm cathode resistor.

[PRR]

Nearly 6 years ago, a Steve_P here was talking about a 50L6 Guild.
https://el34world.com/Forum/index.php?topic=16044.0
A few good pictures down-thread and then nothing more.

Let's Talk Guild thread on a 50L6 Guild with more pictures:
http://www.letstalkguild.com/ltg/showthread.php?178813-55-Masteramp-66-interior-chassis-photos-%28lots%29

[Steve_P]

Nearly 6 years ago, a Steve_P here was talking about a 50L6 Guild.
https://el34world.com/Forum/index.php?topic=16044.0
A few good pictures down-thread and then nothing more.

Let's Talk Guild thread on a 50L6 Guild with more pictures:
http://www.letstalkguild.com/ltg/showthread.php?178813-55-Masteramp-66-interior-chassis-photos-%28lots%29

Right, That was me. I haven't talked with Zizala in a while, but she wasn't a tech type. I got a bad taste in my mouth when you kept insisting that it was transformerless and you would not accept that *that* particular model had a power transformer. All the 53-54 50L6 models do. It wasn't until 55-57 that they lost the power transformer. In all cases until Guild dropped the 50L6gt for the 6V6, these amps were fullwave rectified, via a 35Z5 and a couple of selenium diodes rectifying the other half of the B+.


So, back to the original question, which was, "Are there different power requirements for a p-p amp isolation transformer than an SE amp?'

[sluckey]

So, back to the original question, which was, "Are there different power requirements for a p-p amp isolation transformer than an SE amp?'

I never saw that question. The answer is easy though. NO.

[Steve_P]

Thanks, slucky! I didn't think so, but I thought I would ask. Of the three or four I've seen of these, each circuit is different, except for the tonestack, the tubes and the tremolo channel switching. The Triad FD8-120 Transformer looks like a good solution at 100 VA and a center tap on the secondary.As soon as I can draw out a professional looking schematic, I'll post it up.

[Steve_P]

So, back to the original question, which was, "Are there different power requirements for a p-p amp isolation transformer than an SE amp?'

I never saw that question. The answer is easy though. NO.

Looking at the initial post, I could have been clearer, that's for sure.