What if a BeePre and a SR45 had a baby?

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After a busier winter than expected I am now finally assembling my PT-7 based SR45.

PT-7, C-7X PS choke, 4500ohm Prototype 3.0 OT-2s & PC-3 prototype 2.0 40H 35mA that PJ traded me and SR-45 PCBs PB made me.

After populating the top plate for the first amp I decided to write myself assembly instructions. So I have been going back and forth between the Paramour II, PMII iron upgrade and BeePree manuals and schematics and I couldn't help wondering something.

El84s and 6CM7s both have 6.3v heaters at 760mA for EL84s, 600mA for 6CM7s.

Why not use the PSU DC heater boards from the BeePree I disassembled for the PT-7s, to DC heat the 6CM7s in the SR-45?



 
The BeePre DC heater board has a sort-of low dropout DC regulator that you could set for 6.3V, but you'd need more AC voltage than the 6.3V winding can provide to get that to function properly.  Also the EL84s in the BeePre 1 are AC heated, and the BeePre 1 uses a voltage doubler to make ~13V DC or so that's regulated to 10V for the 300B and its filament bias resistor. 

There are a zillion ways to skin a cat, so I'm sure we can think of a way to integrate those boards if they are something you really want to use!

-PB
 
Sorry to butt in, but would one of you please say more about the SR-45 PCBs?  I have some EXO-45s waiting (with sooo much other stuff!) to be put to use.
Thanks,
Pete
 
A long time ago I made some PC board that could mount above the PT-2 power transformer that went in the Paramour monoblocks, and this board would hold almost all the components necessary for making a SR-45 amp.
 

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Tubegopher said:
OK, you have got my interest. Are there enough of us to be able to get this off of the ground?
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No.  This is one of those products where 10-20 people say they want a pair, and 5 end up ordering.  The demand for 2W 45 amps is very low, and I am available to modify a Stereomour kit into this configuration for the few who are interested.
 
Paul Birkeland said:
The BeePre DC heater board has a sort-of low dropout DC regulator that you could set for 6.3V, but you'd need more AC voltage than the 6.3V winding can provide to get that to function properly.  Also the EL84s in the BeePre 1 are AC heated, and the BeePre 1 uses a voltage doubler to make ~13V DC or so that's regulated to 10V for the 300B and its filament bias resistor. 

There are a zillion ways to skin a cat, so I'm sure we can think of a way to integrate those boards if they are something you really want to use!

-PB
Click to expand...

I would like to use them if they would be beneficial. Primarily because if I don't figure out a use for them while I'm doing all of these rebuilds now, they will end up in my parts closet as spares for a decade. And I'm trying to use and decrease the parts in the parts closet. Not add more parts to it.

And I don't have plans to build another BeePree I anytime soon.

Still have the TFA-2004 Paramounts and OT-1/PT-2 Paramours to build. And then I want to combine my Speco SEX and MQ SEX amps into a pair of push pull monoblocks. Along with a couple Dynaco ST70s and a Scott Pre I've needed to rebuild for years.




 
There's a 5V version of the 45 (183) and you could bridge rectify a 6.3V winding and set the BeePre 1085 regulator to put out about 5.8V (931 ohm resistor would be changed to 456 ohms).  That'll give you about 5V DC for the 183 filament and you could build an SR-45 circuit around that.
 
Sounds like a heavyweight contender for the second pair of SR45 amps.

In fact it may have just bumped the SEX amps out of contention for the belt.
 
2wo said:
I used AC on the 6CM7's works well..John
Click to expand...

I'm sure it will.

I was just trying to come up with a way to use spare parts. And not paying close enough attention to the schematics while doing so at 2AM.

Got the safety ground installed last night. So construction is officially underway.

 

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The schematics (there are two different ones) are not so much proprietary as unsatisfactory. The original design dates from 2007 and was based on the Paramour II using its PT-2 power transformer and the Magnequest upgrade transformers. At first it was just a proof-of-concept idea, with several compromises in the design due to limitations of available components. We released a version - I'm not sure when but around 2011 I think (?) - as a beta with some notes but no actual manual, for experienced and knowledgeable builders/experimenters.

In 2014 I revised the design to use the then-new PT-7 (now PT-10) which among other things increased the shunt-reg current, which in turn required a shift to the 6DN7 as driver/shunt reg. That never went anywhere, though a few ideas went into the MonAmour. It was still unsatisfactory enough that I was reluctant to distribute the design. Somewhere around that time, PB did some work on it including the PC board.

I took one more look at it in 2014, hoping to make a fancy (expensive!) design which could use a 2A3 or a 45, had larger heat sinks and better ventilation, time delay relays for warmup, DC heaters for the DHT, etc. I still could not make a satisfactory, robust design. A few more ideas did make it into MonAmour.

That's my memory, anyhow. YMMV.
 
I will ad that when I build a shunt regulated 45 amp, I make some substantial changes to better optimize the design for 4K-5K iron.  This is more allowable with the PT-10 and its universal primary winding.  Having a PT-7 and trying to run it on low AC line voltage can be problematic unless you lave a good amount of compliance in the high voltage regulator.
 
Thank you PJ and PB.  If I promise not to build it as is, would it be possible to have a peek at a schematic?  ;-)
 
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