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Old 11th March 2010, 01:46 PM   #131
markusA is offline markusA  Sweden
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atmasphere already told us one post above.
VB-408.
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Old 11th March 2010, 02:11 PM   #132
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Originally Posted by atmasphere View Post
Its a VB-408- A high voltage regulator. We found that we had to use them when the amp had the switch in the class AB position. There was so much variation on the plate of V4, the regulator was needed to make the amp play right.

If you use a 3K 3watt resistor instead, the amp will work perfectly as long as you do not include any of the 'class AB' elements shown in the schematic.

The history is that when this amp was made, we had a distributor that wanted the extra feature installed. No-one ever seems to have used it. Fortunately, we're not involved with that mess these days and so we just do the 'class A' circuit exclusively. For that, the resistor above works fine- from 107 to 125V you cannot measure or hear any change in performance of the circuit.
atmasphere,

Excellent! Thank you for the component-ID as well as the history of the sub-circuit. That sort of background is incredibly useful, providing insight into the design process for those of us who are students of the art of engineering.

Configuring the M-60 in "hot-rod" mode (i.e., no Class-A/Class-AB switch) greatly simplifies the power-supply schematic, permitting me to omit the Class-AB "half-power" configuration of the power-transformer primary circuits. The siimplification means that we can also delete the relavent resistors from the bias voltage-divider circuit for the output stage. So, only full-throttle, fire-breathing, Class-A2 M-60's for us!
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Old 11th March 2010, 02:16 PM   #133
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Originally Posted by markusG View Post
atmasphere already told us one post above.
VB-408.
Yeah, that's part of the fun of asynchronous communications...

The "good news" is that, since I can now delete the "Class-A/Class-AB" circuitry, I get to seriously simplify the power-supply schematic. Without the additional complexity, I may be able to complete the power-supply schematic yet today...
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Old 11th March 2010, 02:22 PM   #134
markusA is offline markusA  Sweden
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Cool
It'll be very interesting to see what you've come up with.
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Old 11th March 2010, 02:56 PM   #135
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Default M-60 OTL Power-Supply Schematic (v1.0)

Here's the first-draft of the M-60 OTL power-supply schematic for this thread. I have incorporated the changes that have accrued during the discussion, including "hot-rod" mode (deletion of the Class-A/Class-AB switching), deletion of the B+ regulator for the driver stage, power-supply rail-decoupling capacitors, etc. It's like Ragu Spaghetti Sauce, "It's in there...".

I'm posting both the JPEG and PDF versions of the M-60 "hot-rod" power-supply schematic; the JPEG is potentially a bit marginal on the display resolution presented (but it meets the forum's file-size requirements), so the PDF will offer a clearer view of the schematic in those cases where the JPEG is insufficient.

Let the fun begin...
Attached Images
File Type: jpeg m-60-power-supply-schematic-v1.0.jpeg (169.3 KB, 663 views)
Attached Files
File Type: pdf m-60-power-supply-schematic-v1.0.pdf (186.7 KB, 187 views)
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Last edited by mullardel34; 11th March 2010 at 03:04 PM. Reason: minor word-smithing...
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Old 11th March 2010, 03:22 PM   #136
markusA is offline markusA  Sweden
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Awsome.

It's only now that it hits me. There is some serious hardware going into this build.

7... yes seven separate transformers per monobloc.
Thats 14 transformers per stereo pair.

Gawd da*n that's a lot.

The shematics are clean and simple however so even n0ob like me should be able to pull it off.

No need for PCBs either, always a plus for the DIY crowd.
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Old 11th March 2010, 05:17 PM   #137
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Originally Posted by markusG View Post
Awsome.

It's only now that it hits me. There is some serious hardware going into this build.

7... yes seven separate transformers per monobloc.
Thats 14 transformers per stereo pair.

Gawd da*n that's a lot.
Agreed! Fourteen power-transformers is quite a pile of energized iron, isn't it?

The power-supply clarification from "atmasphere" (regarding the total voltage applied to the output stage tubes) did allow me to delete a second output-stage power-transformer that I had originally thought would be necessary. But those filament heater power-transformers just keep multiplying like rabbits...

None of the usual toroidal power-transformer vendors (Plitron, Avel-Lindberg, Antek, etc.) offer any 6V models with a higher current capacity than the 50VA-rated units specified, so we have to parallel the filament transformers. Then I had to add one more to allow the inter-dependent application of the filament power ("Standby" mode) and the high-voltage power ("Operate" mode).

Quote:
The shematics are clean and simple however so even n0ob like me should be able to pull it off.
Thanks! I was trying to visually convey the elegant simplicity of even the power-supply of the M-60. As you've noted, there's really nothing terribly complex here, just a very large number of components to harness.

Quote:
No need for PCBs either, always a plus for the DIY crowd.
Yes, I prefer to construct my DIY projects using a point-to-point wiring methodology. Those IAG single-socket terminal-boards really make the assembly straightforward as well as provide a really nice look-and-feel to the guts of our projects. The point-to-point approach greatly facilitates the inevitable modifications in a clean, non-destructive manner.
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Old 11th March 2010, 07:46 PM   #138
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Default M-60 OTL Revised Signal-Path Schematic

Now that we've got a first-draft schematic for the M-60 power-supply posted for review, I'll start work on the complementary revised M-60 signal-path schematic that reflects the "hot-rod" M-60 configuration (deleted Class-A/AB circuitry, increased bias current for the input-stage, etc.). I'll crunch the diagram as soon as time permits...
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Old 12th March 2010, 05:05 AM   #139
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That 75V AC rating on the secondaries of the B+ supply for the output tubes seems a bit low to me. Typo?

Stancor used to make a 20-amp filament transformer that did the job nicely, but it didn't have a 235V capability. The Hammond 266V6B is rated at 20Amps also.
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Old 12th March 2010, 07:49 AM   #140
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Stancor TGC175-12 (28A@6.3V) and TGC130-12 (20.60V@6.3V) looks to be in the right area.

But wasn't the T2 supposed to be two separate transformers? Not just separate secondaries?
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