Lavane
Lunatic Member
Then it must be the low gain version.
A box arrived.
- Thread starter Lavane
- Start date
Pio1980
AK Member
12AU7s, standard gain version.
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Does your version use the 12AU7's or 12AT7's?
Lavane
Lunatic Member
Its the 12AU7 version.
Lavane
Lunatic Member
I've gone about as for as I can go until the paint dries on the transformers. I'll probably add the sockets and other bits to the second chassis in the meantime.
I was going to swap power switch and RCA jack, but the hole for the power switch is larger and I don't like how the RCA jack fits in the larger hole. Plus I would have to take a drill to the rear of the chassis.
I was going to swap power switch and RCA jack, but the hole for the power switch is larger and I don't like how the RCA jack fits in the larger hole. Plus I would have to take a drill to the rear of the chassis.
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hm, that doesn't really make sense to me. Everything I know about parallel tubes (which is limited, admittedly) is that they want half the plate load as non-parallel, so if this is 4k plate to plate for single, 2k plate to plate for parallel makes sense.
Lavane
Lunatic Member
I will be running a quad instead of just two, but ya, it doesn't make sense. Here is the schematic sent with the instructions.
Lavane
Lunatic Member
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.
That is a whole lot to ask out of a single rectifier tube. Quick look at the datasheet tells me thats going to want more than double what a 5ar4 can provide at full power, and most of what it can provide just at idle. This really needs to be solid state rectified.
Legrace
Super Member
My M125's see a lot of use, typically 8-12 hours per day. They really are a joy to listen to. What I found took them to the next level for me was incorporating autobiasing modules. Most significantly in terms of improved stability. Rectifiers esp are pushed really hard in these amps. Why you so often see SS rectification being recommended for use in these, as most modern tube rectifiers will simply go pop in these amps. Something you learn fast if you don't know otherwise, as in my case. Lost my first tube rectifier within 2 weeks. So good move on the part of the OP to go SS right off the bat.
Another issue I had with the stock build, maybe twice a year on average, was power tubes red plating. Infrequent enough not to pose a major headache, but definitely not liking impact on my tubing expenditures! Fortunately this is no longer an issue, as post AB has seen a total cessation of red plate events or rectifier arcing going on almost two years now. Plus its really nice now not having to futz with manual bias trim pots. (removed during this upgrade) Plus I like the little leds that inform whether the tubes have biased up properly post startup, nice feature. Getting way more hours out of my tubes now, so in time this mod actually pays for itself.
For tube complement running KT120, RCA clear tops for driver tubes, and gZ37 tube rectifier. Splendid results for SQ.
Quite possible my experiences are a non issue with latest kits or were self inflicted due to sloppy workmanship on my part. Above is just fyi should any similar quirkiness ensue, and what I did to resolve. Have fun and enjoy these great amps!
Another issue I had with the stock build, maybe twice a year on average, was power tubes red plating. Infrequent enough not to pose a major headache, but definitely not liking impact on my tubing expenditures! Fortunately this is no longer an issue, as post AB has seen a total cessation of red plate events or rectifier arcing going on almost two years now. Plus its really nice now not having to futz with manual bias trim pots. (removed during this upgrade) Plus I like the little leds that inform whether the tubes have biased up properly post startup, nice feature. Getting way more hours out of my tubes now, so in time this mod actually pays for itself.
For tube complement running KT120, RCA clear tops for driver tubes, and gZ37 tube rectifier. Splendid results for SQ.
Quite possible my experiences are a non issue with latest kits or were self inflicted due to sloppy workmanship on my part. Above is just fyi should any similar quirkiness ensue, and what I did to resolve. Have fun and enjoy these great amps!
Lavane
Lunatic Member
The autobias boardss are no longer sold by VTA. Too many failures of the board. One person even added a regulator board connected to the autobias board.
Lavane
Lunatic Member
It shows a rectifier tube in the schematic, but lists a WZ68 SS rectifier. I have a couple of the WZ68's. I think I'm going to remove the copper top and drill some holes near the bottom and top to get a bit of air flow. They do run hot. Man I wish a tube company would produce GZ37 rectifiers. You would think there would be enough demand.
Legrace
Super Member
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/
trainbuftony
Electron Herder
I remember you having that red plate issue
Multiple people gave you specific instructions on how to diagnose and fix it, which you ignored in favor of a band aid which doesn't work, cant work, (auto bias board).
As for the ss rectifier that's smart.
Modern tube manufacturers could build a bigger badder rectifier but that's going to get more people in trouble than it's going to help.
In order to get the B+ current, you need to produce lots more filament current.
If you're going to design around more filament current, buy 2 or 3 5AR4s and you'll soon realize the tubes are the cheap parts.
The expense is in the massive copper and iron core needed for a substantial increase in performance.
Let me extend the invitation to hook them up on my distortion analyzer and do a full power bandwidth test into a dummy load.
I'm sure one or two folks would like to see the results.
Legrace
Super Member
I appreciated the suggestions at the time, just that I saw multiple additional benefits to be gained with pursuing the AB path. Like eliminating manual bias adjustment. Now the amps ramp up to the bias set point within one to two minutes, after which they never deviate one iota, day in day out, month after month. Like night and day comparing to the oscillations of before.
What I have to come to understand is that in this hobby purists abound, and for those adding circuitry of this type is verging on sacrilege. The fact remains I have not had a single red plate occurrence since installing these boards. After 6 months I was hopeful, after a year confidence really was growing, but still not quite ready to declare victory. Factor in several additional months of trouble free operation and now I'm sold. My amps are rock solid ever since, which to me meets the definition of a successful fix. I'm sure there were other fixes that I could have applied, but they would not have delivered the many additional benefits provided by the AB boards. Proves the old adage again; there's more then one way to skin a cat.
trainbuftony
Electron Herder
Reason for that is that the tech who installed the boards found and fixed the fault.
That's what techs do.
Pull a transmission out of a truck and find a broken flex plate, you are going to replace both the trans and the flex plate.
When you hired the tech to install those boards he would have been remiss if he didn't check all the things we told you to check.
No doubt he found the fault, and also, the customer is always right. I feel 100% confident saying those boards didn't fix your amp. They had nothing to do with it.
The Tech fixed your amp.
He had to do that, likely for free, understanding the work you requested he do, was not going to be effective unless he made the repair.
Now back to your regularly scheduled programming.
That's what techs do.
Pull a transmission out of a truck and find a broken flex plate, you are going to replace both the trans and the flex plate.
When you hired the tech to install those boards he would have been remiss if he didn't check all the things we told you to check.
No doubt he found the fault, and also, the customer is always right. I feel 100% confident saying those boards didn't fix your amp. They had nothing to do with it.
The Tech fixed your amp.
He had to do that, likely for free, understanding the work you requested he do, was not going to be effective unless he made the repair.
Now back to your regularly scheduled programming.
Legrace
Super Member
Except that I installed the boards myself, and that was the only change I made. Next time suggest you verify your facts first.
From what I understand adjustable fixed bias designs are inherently more prone to instability versus classic cathode bias schemes. Clearly the algorithm incorporated into these boards is highly effective at compensating this instability. The OP may never find a need, but given the many benefits should problems arise, this is an approach definitely worth considering.
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