lGl-2, continuing "hybrid madness" - no GNFB class A

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#121
Just in case - looking at the tube from the top (e.g. through the tube), this is the right pins numbering.
 

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#125
This upside-down board thing is adding a whole new twist to the sport! voltage is pretty close on R3 and R10 when I first flip the board over to measure. I think I'm watching the tube cool. It drifts all over the place when they are upside-down. They quickly settle when right side up.😀
 
#129
I tried to figure out how I managed to have voltage on the input of these. With the tube installed backwards it looks like the input would have actually been an output. It must have oscillated to actually put out voltage. Did a good job on my scope! Pushing 250V back into the signal generator didn't go well!😱
 
#133
Thanks Jeff,

I did see that the tube socket was reversed. I was looking at the board and it looks like most of the parts could just be mounted on the bottom as well. I'm thinking only the IC would have to be mounted on the silk side so that is not a deal breaker. I have only scanned through the thread so far.
 
#134
Hi Jeff,

I've had a little while to look things over. I'm trying to put a Mouser order together and I have some questions.
1) Is there a schematic that matches the part numbers for your layout?
2) On the 250V PSU board, you have a specific layout for the bridge. Do you have a part number for that?
3) How critical is the 250V? Is there a range? What VA is needed?

Thanks, Terry
 
#135
Hi Terry, I've got a well-working prototype, built with my initial layout, as shown >HERE<. Tubes are at the top side then.

If you've got the boards with Jeff's layout, then the tubes must be placed at the bottom (upside down).

With regards to OPS. This front-end is no-global-feedback, so OPS has to be low-distortion one. The best result is shown with the Hex-FET SlewMonsters - IRFP240/9240 pairs at the output. Warm tube sound 🙂

Regulated PSU is important here (careful with high voltage).
Also note - some capacitors have to be tather high-voltage rated (250-400V).

Cheers,
Valery
 
#136
still4given said:
Hi Jeff,

I've had a little while to look things over. I'm trying to put a Mouser order together and I have some questions.
1) Is there a schematic that matches the part numbers for your layout?
2) On the 250V PSU board, you have a specific layout for the bridge. Do you have a part number for that?
3) How critical is the 250V? Is there a range? What VA is needed?

Thanks, Terry
Click to expand...

The range of the output DC is actualluy 250-300V 🙂
 
#137
Hi Valery,

Since Jeff was kind enough to share his boards with me I will try to make it work with them. I will probably just flip the boards over and mount everything but the IC on the bottom. I should be able to just rotate the transistors 180 since none of them are thermally coupled. Everything else is just two pin so simple. Only drawback will be the terminals will be reversed from the Slewmaster ops but that is no big deal. I have a 5P Hex-FET Slewmaster OPS sitting here so that should be simple. I have to order some tubes and sockets and a few other items so it will be a week or two before I can get around to building it. I have one of Jeff's cap multiplier boards for the 250v supply so I think I'm good there. What VA does the 250vac transformer need to be?

Thanks, Terry
 
#138
still4given said:
Hi Valery,

Since Jeff was kind enough to share his boards with me I will try to make it work with them. I will probably just flip the boards over and mount everything but the IC on the bottom. I should be able to just rotate the transistors 180 since none of them are thermally coupled. Everything else is just two pin so simple. Only drawback will be the terminals will be reversed from the Slewmaster ops but that is no big deal. I have a 5P Hex-FET Slewmaster OPS sitting here so that should be simple. I have to order some tubes and sockets and a few other items so it will be a week or two before I can get around to building it. I have one of Jeff's cap multiplier boards for the 250v supply so I think I'm good there. What VA does the 250vac transformer need to be?

Thanks, Terry
Click to expand...

No problem, Jeff's boards are nice, we just understood at some point that he's got the tube pins numbered in opposite direction.

Transformer I use is a small 15W toroid, giving both 240V AC (0.05A) and 6.3V AC (1A). Designed for tube guitar pre-amps.
 
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