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May 25, 2019, 04:10:49 am

Author Topic: SR 45 rebuild  (Read 583 times)

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Offline awsjr

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SR 45 rebuild
« on: February 20, 2018, 08:05:37 am »
I went from the Paramour II 2A3 to 45 to SR 45...  want to do a clean rebuild for the SR 45 and have a couple questions...

I currently have (3) 47uF capacitors in my amp and the SR 45 schematic shows 2..
Paramour II manual page 31 (1) goes to P4U - P5U and (1) goes to P10U - P11U
the iron upgrade manual page 7 states to maintain proper B+ add an additional 47uF to P8 - P9 and a 1300r to P9 - P11 if converting from the 2A3 to the 45 tube... and again the SR 45 schematic does not show this,,, can someone please confirm what it should be..

also are there newer circuit boards to use ?.. thought I saw a while ago the board was redesigned...

biggest change is I would like to use an EXO-45 Ni opt and a CP-06006 plate choke 40 madc, 50 H, 550 ohms dcr, instead of the BH-5 & BH-6
thanks in advance for any help with this 
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Offline Paul Birkeland

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Re: SR 45 rebuild
« Reply #1 on: February 20, 2018, 10:12:26 am »
I currently have (3) 47uF capacitors in my amp and the SR 45 schematic shows 2..
Is one of them your cathode bypass cap? (Labeled 100uF/350V on the SR45 schematic)  If it's just in the power supply in parallel with one of the other 47uF caps, it's not doing any harm (but it doesn't have to be there).

the iron upgrade manual page 7 states to maintain proper B+ add an additional 47uF to P8 - P9 and a 1300r to P9 - P11 if converting from the 2A3 to the 45 tube... and again the SR 45 schematic does not show this,,, can someone please confirm what it should be..
The SR-45 schematic assumes that you have the Magnequest PCP-15 plate choke.  This is (as far as I remember), the choke that came with the Paramour iron upgrade kit.  You need to go off the schematic for the SR-45, not the modification instructions for the iron upgrade kit in this case.

also are there newer circuit boards to use ?.. thought I saw a while ago the board was redesigned...
Yes, we have progressed significantly in the decade or so since the SR45 was put out in terms of board design and thermal management, but there's no documentation on how to put these boards into a Paramour in order to end up with a SR45 amp, and I do not believe there is any intention to provide this documentation. 


biggest change is I would like to use an EXO-45 Ni opt
That's not a good selection for the SR-45 circuit.  You really want to stick to the 3K target.  (TFA-2004)  If you can't find TFA-2004s, the stock Paramount transformers are for sale from time to time used on eBay and will absolutely loaf along as an output transformer for the 45. (They will also mount to the Paramour II plates just fine)

and a CP-06006 plate choke 40 madc, 50 H, 550 ohms dcr, instead of the BH-5 & BH-6
BH5/BH6 are for the Paramount, not the Paramour.  The 40mA/50H/550R is a dead ringer for the BH2, and the first couple that were made may have CP-06006 written on them.  You can treat this part as being the same as the plate choke in the schematic for all intents and purposes. 

I would also plug myself a bit, as I have done some SR45 conversions in the past and am available to implement the newer parts/boards.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline awsjr

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Re: SR 45 rebuild
« Reply #2 on: February 21, 2018, 02:42:13 am »
hi Paul...
thanks for your reply...
no, the 100uF bypass cap is separate... the extra 47uF and 1300ohms resistor are in the PS.. CLCRC

you said the "BH5/BH6 are for the Paramount, not the Paramour."... thats confusing as these were sold as an iron upgrade for the Paramour II.... I am not familiar with all the prior Bottlehead products so are you talking about the Paramour vs the Paramour II ?

I do have the BH 5 3K OPT but again would like to try to use the exo-45 and the cp-06006 plate choke..
if I change R1 16.2ohms to reduce the C4S current to 51mA (R1 16.5 ohms) to get the dissipation at 6 watts and the reduce the 10uF parafeed capacitor to ~4uF and the cathode resistor to 1500ohm it should work... or no ?

thanks again





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Offline Paul Birkeland

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Re: SR 45 rebuild
« Reply #3 on: February 21, 2018, 04:10:18 am »
the extra 47uF and 1300ohms resistor are in the PS.. CLCRC

you said the "BH5/BH6 are for the Paramount, not the Paramour."... thats confusing as these were sold as an iron upgrade for the Paramour II....
It's possible that the B+ was reduced to make the 3K Paramount transformers work a bit better in the Paramour II, that would explain your modified power supply as well. I do now see that those transformers were listed as working in both the Paramour II and Paramount, but at the same time I know that Mikey has not wound any 4K output transformers for us.

I do have the BH 5 3K OPT but again would like to try to use the exo-45 and the cp-06006 plate choke..
Well, you can redesign the SR-45 circuit and optimize it for the higher impedance transformer, or you use them as-is and end up with a very, very low power SR-45.The BH-5 is the right transformer for the job, I would suggest using it.
if I change R1 16.2ohms to reduce the C4S current to 51mA (R1 16.5 ohms) to get the dissipation at 6 watts and the reduce the 10uF parafeed capacitor to ~4uF and the cathode resistor to 1500ohm it should work... or no ?
You'll need a regulated B+ of 350V, a different cathode resistor, and to re-balance the whole shunt regulated power supply so that it still functions after these changes.   
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline awsjr

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Re: SR 45 rebuild
« Reply #4 on: February 21, 2018, 04:31:19 am »
thanks Paul..
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Offline tsingle999

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Re: SR 45 rebuild
« Reply #5 on: February 22, 2018, 03:51:59 pm »
I can vouch for PB's PS board for this amp. He put them in mine. Very compact and made the rest of the amp easy to build and even easier for him to rebuild after my shenanigans!
Taran
Macmini tidal masters to BH DAC to Fix to BeePre to SR45BN (with mq dowdy n tfa2004sr) to Abby with fostex FE 166esr and Blumenstein Max Subs

Offline 2wo

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Re: SR 45 rebuild
« Reply #6 on: February 23, 2018, 06:40:50 pm »
In my SR-45 I can switch between  the BH-5 and the ni EXO-45 using the using the BH-6 choke

In my opinion, the BH-5 sounds a bit fuller and the EXO maybe a bit more "precise". They both sound fantastic and I have a difficult time deciding witch I prefer on any given day...John
John Scanlon

Offline awsjr

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Re: SR 45 rebuild
« Reply #7 on: February 24, 2018, 01:42:47 am »
In my SR-45 I can switch between  the BH-5 and the ni EXO-45 using the using the BH-6 choke

In my opinion, the BH-5 sounds a bit fuller and the EXO maybe a bit more "precise". They both sound fantastic and I have a difficult time deciding witch I prefer on any given day...John

hi John.. did you make any capacitor or resistor changes going to the EXO-45 ? I am using a 1500ohm cathode resistor and reduced the cPf cap from 10uF to a 4.7uF...  the boards used for the stereomour II shunt regulator kit could be an upgrade over the older boards and do not look like it would be too difficult to figure out... except got an email indicating the boards will not be sold indiviually for some reason
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Offline 2wo

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Re: SR 45 rebuild
« Reply #8 on: February 24, 2018, 08:08:59 pm »
No, I didn't make any changes other than wire the EXO in with a switch. I think I have 6.8 Parafeed cap in...John
John Scanlon