[fazer]

I’m falling more and more in love with it’s delicious tone

I’ll start rounding up some parts.   I have some 0uncer 016 input with 50k output mic transformers and the 6j7’s.  Plenty of old cases so will need a choke and output trans .   Also have some Modutec VUs I don’t have any old ones.  These have to be 50 years old but nothing that goes back to the 30’s.

[EmRR]

I’ll start rounding up some parts.   

I have original OP-6 inputs in the BM.

I can make the original gain control for anyone wanting that, including modified Daven's that will retrofit a bad original OP-6. 

[DaveP]

I was thinking about using a 6SN7 as the triode with the second section as a CF to replace the 6J5.  It could be a Parallel connection also.  rp is the same as a 6j5 .  Thoughts.

That would work OK, just need a bit more heater current.

DaveP

[mjrippe]

I just posted the schematic of the OP-6's grandpa, the 62-A, in the Tech Docs section if anyone is interested.  I will be scanning the entire manual from 1937 soon.

[EmRR]

I just posted the schematic of the OP-6's grandpa, the 62-A, in the Tech Docs section if anyone is interested.  I will be scanning the entire manual from 1937 soon.

Grandpa is true, interesting to note the 62-A was the budget alternative to the OP-5, and like many other things the fancier gave way to the more inexpensive as things progressed into the 1940's.   I have an OP-4 and an OP-5, both are intended for battery power only.  Have seen the OP-2 and OP-3, nearly scored an OP-3 once. 

[mjrippe]

Complete RCA 62-A manual uploaded here: https://www.dropbox.com/s/hna6milje5hq5xe/62-A%20Manual.pdf?dl=0

[EmRR]

Complete RCA 62-A manual uploaded here: https://www.dropbox.com/s/hna6milje5hq5xe/62-A%20Manual.pdf?dl=0

Wow, that PSU is same concept as the 96-A.  Very surprised to see such complexity in the lower range remote amp, and no similar supply offered with the OP-4/5. 

[DaveP]

mjrippe,

Thank you for that!

Best
DaveP

[mjrippe]

Wow, that PSU is same concept as the 96-A.  Very surprised to see such complexity in the lower range remote amp, and no similar supply offered with the OP-4/5.

Agreed, Doug.  I was sharing this manual with a friend who designs audio gear and mics and we were marveling at the PSU.  Four tubes and DC regulation is a HUGE expenditure at the time.

[rjb5191]

Greetings,

May I ask what type of cable and  power connection did you use between the power supply and preamp?

best,
Ryland

[DaveP]

It was about 5A cable, but the most important thing was the diameter, it had to fit in a Bulgin Plug  313-993
 and socket  313-970.

These are Farnell part numbers, I believe this is Newark in the US.

They were wired HT/B+,  6.3Vdc and Earth/ ground.

Best
DaveP

[fazer]

Hey Dave I have question on the gain switch.  I’m assuming it’s non-shorting.

[DaveP]

I have question on the gain switch.  I’m assuming it’s non-shorting.

I use MBB (Make Before Break) switches for this kind of use to lessen switching noise.

I use BBM types when switching B+ on meters.

Hope that answers your question, happy 4th of July and stay safe!

DaveP

[fazer]

Thanks Dave.   We are all safe.   I ordered the shorting type. 

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