VAC 70/70 mk3 tube rolling question

One pair 6SN7 are for the gain stage, the 2nd pair are the phase inverters.
Example; RCA L, R gain stage.
Raytheon L, R phase inversion (drivers for output tubes)

Typically; being certain to not use the exact same tube for the first two stages (same channel) of your power amp, will provide a better presentation.     The most referred to 6SN7 comparison (http://www.dehavillandhifi.com/6sn7_vt.htm) mentions the practice of mixing things up, about three paragraphs from the bottom.     More opinions on 6SN7s, here: https://www.head-fi.org/threads/the-reference-6sn7-thread.117677/      No doubt, someone will mention the Melz tubes.     You might want to refer to this thread, regarding their noise, reliability, etc:  https://forum.audiogon.com/discussions/shootout-of-nos-6sn7-tubes?highlight=6sn7%2Bshootout    I guess they can be a nice tube, if you get lucky! 

Use matched set of Rca, matched set Raytheon.

The input circuitry of the Renaissance Seventy/Seventy is derivative of the unique Williamson circuit, which provides pure, direct coupled, inherently balanced input amplification and phase splitting. Type 6SN7/5692 octal twin triodes do the honors.

https://skyfiaudio.com/products/vac-valve-amplification-company-renaissance-seventy-seventy-70-70-du...

@lowrider57  Thanks for the helpful information. Forgive me as I don't understand all the details of the williamson circuit and I can't upload photos here. 

So basically there are four 6sn7 tubes in the front row of 70/70. Assume they are V1, V2, V3, V4 from left to right. My understanding is that V1, V2 are for channel 1, and V3, V4 are for channel 2, is that right?

My question is which ones are for gain stage and which ones are for phase inverters? ( If my above assumption is right, is v1, v3 for gain stage; v2, v4 for phase inverters ?) Thanks!  

Correct, V1,V2 for left channel.
V3,4 for rt. channel.

Sorry, I can't help identify which is gain and which is driver. Hopefully a VAC owner will chime in.
But, designers like to keep things organised, so I would guess that the gains are V1 and V4. Or they could be V2 and V3.

Have you looked for a user manual online?

Call the VAC factory and speak to Kevin or Brent. I believe the order will be the two most outside (L and R) should match and the two inner should match, but my memory may be incorrect.  They are always happy to welcome new members into the VAC family and will share where they believe each pair will work best (splitter or gain) and exactly which pair of tube sockets is each... so yes one of each for each channel but you need to know which sockets are what in the circuit. If your “red base” RCAs are the 5692 military versions I would suggest those to be in the amplification section and use the others as the splitters.
The manual is on the VAC website if you have not already seen it. http://www.vac-amps.com/manuals/Manual_Ren70-70.pdf

@rodman99999  Thanks a lot for these info! I purchased my two pairs of 6sn7 from Brent at audiotube.com. He helped me picking up those sets. Personally I don't have a lot of experiences with tube rolling. 

@lowrider57  Yes I checked the user manual online here: http://www.vac-amps.com/manuals/Manual_Ren70-70.pdf

Unfortunately the Figures that shown the tube placement are missing. (figure 2).

@drrsutliff  Thanks for the info! Too bad the figures that are showing which socket is which are missing in the online manual. I sent Kevin an email asking about the placement. Hope he can get back to me soon. 

Good luck, @yuhengdu_tiger . You have a beautiful amp. And your 2 sets of tubes should work well together.
🤞 fingers crossed.

@lowrider57  Thanks! I came across this ad https://www.canuckaudiomart.com/details/649558669-vac-valve-amplification-company-renaissance-7070-mk-iii-mint/ and by checking at the pictures my best guess would be that V1, V4 are phase inverters and V2, V3 are gains. 

@yuhengdu_tiger .
Yes, I agree. Nice work finding that pic.

over the years i have found kevin hayes to be approachable, welcoming and very helpful in all inquiries regarding his gear

one of the really good guys in the biz, and makes lovely (if pricey) gear

Almarg, where are you?

@roxy54 
Almarg is no longer a tube guy, no more VAC. Can you believe it?
Of course, his wisdom is always welcome.

That is not good news Tvad. He's a great contributor and a good man. I truly hope that he will be well soon. I realize now that I haven't seen any posts from him lately.

Lowrider57,
I was aware that he no longer had his VAC, but I also knew that he would be a wealth of good information about it.

@roxy54 ,, 
Oh yes, I was agreeing with you.

I wish Al all the best, he is sorely missed on the forum. My thoughts go out to him for a speedy recovery.

Wishing best recovery for Almarg. Such a smart and knowledgeable guy not to mention patient  giving, humble and the model gentlemen always. A real mensch. Hope to see him back here soon. One of a kind and one of my favorite people.

Yes a fantastic gentleman:-) Godspeed on healing !!!!!!

It goes without saying to anyone familiar how many people almarg has helped with their home audio issues here. Not only that, but he goes out of his way and spends time to do the proper research on products before speaking. His attention to detail is impeccable.  Best source of charitable yet reliable and unbiased audio advice that I know of. His absence leaves a real hole here I would say and hope he is back very soon.

He has helped me many times on and off this forum, and I have the utmost respect for him as a person.

@lowrider57  I heard back from Kevin this morning. Actually it is V1 and V4 are drivers and V2 V3 are phase splitters. Here is Kevin's response:


"Yes, it is perfectly fine to mix brands of 6SN7. In your scenario, use one brand for the V1x positions, and the other for the V2x positions.

Technically, 6SN7 GTA or GTB types should be used, but we have not heard of any significant problems with earlier NOS version, although they do have lower maximum ratings.

With respect to matching, when operating the 70/70 with zero negative feedback, matching the gains of the tubes between the left and right channels helps to keep the center image centered. Section matching within each V2x tube is desirable but not highly critical."

Anyone needs the diagram he send me, I can also email to you if needed. 

Interesting and valuable info.

The RCA red base is a 5692 which requires less voltage. But it's good to hear VAC is ok with running all versions of the 6SN7.

Hi, I just received a VAC 70/70 iii, and this thread is great!

I have a question:  could I drop the Psvane CV181 T Mark ii in as driver tubes?  I have a pair of these, and I'd love to hear how they sound in place of the EH currently in there.

I don't know if they're 6SN7A, 6SN7B or something else that is 6SN7 ish - I don't want to mess up the amp, since it just came back from service.

Thanks!