A box arrived.

[Lavane]

Mostly apples to early version of the board. Has since been updated and incorporates a number of fixes. One of the more significant changes was the addition of an on board isolation transformer. I waited for the newer version to be released as was aware of the issues with the original board. Per my post the updated board has been trouble free.

Current SOS is below (no affiliation). On their website they indicate they are exclusive NA agent for these. I rather suspect this is a larger factor in why VTA no longer offer this product.

https://www.erhard-audio.com/

Thanks. Ill take a look at it. Erhard Audio uses them. I daw one person built a regulator board fir the earlier version.

 

[Lavane]

Lavane, I have a WZ68 in my VTA ST 120 that I have ventilated. Six holes , three on each side opposite one another and another in the top. Runs quite cool and an easy and meaningful modification.

Thanks for the info. From the info I could find, these can be prone to failure without ventilation In some applications. How did you remove the cover? I was thinking carefully cutting through the glue around the bottom with a razor knife.

 

[Lavane]

Looking over the wiring diagram and wire routing, I just couldn't bring myself to mount the power switch on the front and input jack at the rear. So I went ahead and mounted the RCA jack on the front and power switch on the back. This will make for very short runs for both the AC switch and input. I use remote controlled outlets already for my ST-70 and ST-35.

 

[Legrace]

Relocating power switch to back is a good idea. Some other ideas worth considering:

http://ielogical.com/Audio/VTA_M-125.php

 

[Lavane]

Relocating power switch to back is a good idea. Some other ideas worth considering:

http://ielogical.com/Audio/VTA_M-125.php

Thanks. Ya, I've read through it several times. I'll probably terminate the 5v winding along with a few other things he did.

 

[Lavane]

The transformers baked in the sun yesterday.
I was going to leave them out in the sun another day, but a bird already crapped on one. I like using epoxy appliance paint.

 

[tonyg88]

The transformers baked in the sun yesterday.
I was going to leave them out in the sun another day, but a bird already crapped on one. I like using epoxy appliance paint.

I thought that kind of stuff only happened to me... lol. Looks good!

 

[Legrace]

Thanks. Ya, I've read through it several times. I'll probably terminate the 5v winding along with a few other things he did.

The pics on the ielogical web pg reflect the early AB board. Ones I installed below. The addition of the isolation transformer to the left is visually most obvious difference, well that and the absence of a corporate logo that was screened onto the early version.



Sorry to hear abut the bird crap. My issue usually is insects landing on the paint.

 

[Lavane]

The pics on the ielogical web pg reflect the early AB board. Ones I installed below. The addition of the isolation transformer to the left is visually most obvious difference, well that and the absence of a corporate logo that was screened onto the early version.

View attachment 2177073

Sorry to hear abut the bird crap. My issue usually is insects landing on the paint.

Was the issue with the older board with just certain amplifiers, or with pretty much anything it was put into, do you know? I'm just glad I never tried one of the older versions. And ya, bugs are a problem here later in the spring.

 

[Legrace]

Was the issue with the older board with just certain amplifiers, or with pretty much anything it was put into, do you know? I'm just glad I never tried one of the older versions. And ya, bugs are a problem here later in the spring.

Ya not always good to be an early adopter. As far as the extent of the issue am not aware. Just glad they eventually worked out the bugs, has made such a difference to my enjoyment of these amps. I will never go without auto bias ever again.

 

[8xlaxx]

Looking over the wiring diagram and wire routing, I just couldn't bring myself to mount the power switch on the front and input jack at the rear. So I went ahead and mounted the RCA jack on the front and power switch on the back. This will make for very short runs for both the AC switch and input. I use remote controlled outlets already for my ST-70 and ST-35.
View attachment 2176828 View attachment 2176828

Yes, odd question....

What is the distance from the edge of your workbench to the pegboard? Do you find that there is enough room to work and repair there? Thanks.

 

[Lavane]

Yes, odd question....

What is the distance from the edge of your workbench to the pegboard? Do you find that there is enough room to work and repair there? Thanks.

Just enough. I've had larger pieces of equipment on it. I never have more than one project on it at a time though. I have two tall shelving units on either side that holds other equipment and test gear. There are two long benches out in my garage, but no heating or air, so I built the small bench to fit a small back bedroom. I've had large receivers spread out on it without any problems working around them.

 

[Legrace]

Thanks for the info. From the info I could find, these can be prone to failure without ventilation In some applications. How did you remove the cover? I was thinking carefully cutting through the glue around the bottom with a razor knife.

After losing several 5ar4 in quick succession I then switched to copper tops in my M125's. They get really hot, which can indeed lead to failure of these as well despite them being SS, so adding ventilation holes is a good idea. To remove the cover all I did was run the amp for awhile until up to temperature. Then a slight tug on the cover and it pulled away no problem. Wearing gloves of course and right after shutting the amp off. Later on I scored a few GZ37's which is what I'm running today, that is one stout tube.

 

[Pio1980]

They will be the biggest tube amps I've ever had. The one in my avatar is only 5.5wpc. The best sounding preamp I've ever had is the Erhard's Ella. I really like it. I've had several TOTL 70's Marantz SS systems, but have sold most of it.
My ST-70 has been my best tube amp so far. Now I'm watching paint dry on the transformers for the M-125's. I've had a few 75wpc to 125wpc SS power amps, but nothing that big in tubes until now.

Dyna ST-70 or VTA ST-70?

 

[8xlaxx]

Just enough. I've had larger pieces of equipment on it. I never have more than one project on it at a time though. I have two tall shelving units on either side that holds other equipment and test gear. There are two long benches out in my garage, but no heating or air, so I built the small bench to fit a small back bedroom. I've had large receivers spread out on it without any problems working around them.

Thank you. My bench is about the same depth as yours and would like to come up with some ideas to mount / use a o-scope, signal gen., etc that is easy to reach.

Carry on with your project,...no intentions of hijacking.

 

[daveshel]

Looks like a fun project! Happy building.

 

[Lavane]

Dyna ST-70 or VTA ST-70?

VTA

 

[Lavane]

After losing several 5ar4 in quick succession I then switched to copper tops in my M125's. They get really hot, which can indeed lead to failure of these as well despite them being SS, so adding ventilation holes is a good idea. To remove the cover all I did was run the amp for awhile until up to temperature. Then a slight tug on the cover and it pulled away no problem. Wearing gloves of course and right after shutting the amp off. Later on I scored a few GZ37's which is what I'm running today, that is one stout tube.

Thanks, I'll give that a try. If GZ-37's weren't so expensive I would probably use them.

 

[Lavane]

Thank you. My bench is about the same depth as yours and would like to come up with some ideas to mount / use a o-scope, signal gen., etc that is easy to reach.

Carry on with your project,...no intentions of hijacking.

I do have a shelf on top of the pegboard. It holds my scope and a few other testers. The rest I just keep on the shelves next to it and drag them out when needed. On the sides of the shelving I have my dim bulb taeter mounted and some big hooks to hang soldering irons, cabling and other test leades. With limited space, the smaller, cheaper tone generating boards, diode/capacitor/resistor testers, etc., are handy. I don't even use the signal generator I have much anymore. It's just easier to grab the small signal generator board kit I bought, or use a phone app. I have another small unit that plugs into the wall and gives me voltage, wattage and amperage draw. I use it with my variac.

 

[sKiZo]

I was lucky enough to score a couple GZ37's for $80 each when I built my ST120. Still running the same rectifier five years later.

Does BobCo offer an octal version of the amp yet? I adapted mine to run a 6SN7 in the center spot with excellent results. The stock iron also provides plenty spare power to drive a trio of those AND a quad of KT120's

Oh - don't quote me, but I believe the "yellow sheet mod" works with the M125 as well. Real simple change that prevents reverse flow that can kill a rectifier with the addition of a couple inexpensive diodes. Also, the Weber WZ68 is bulletproof - I've got one of those as backup here.