Building a 6SN7 SRPP preamp kit.

Tleung

Senior Member
One of my audio buddy ask me to help him to built a 6SN7 preamp. He want it to look more convention preamp. We had been searching online and found this company.
Analog Metric - DIY Audio Kit Developer and he bought the 6SN7 SRPP kit with power transformers. We went over the kit components and decided to upgrade few of the parts. All the parts arrived and I started to assemble the kit. This is kind of different way I use to build. The website provided you with all the schematic and BOM and installation instructions. 6SN7 SRPP S2 Preamplifier Kit Set (Stereo)_Preamplifier Kit Set_Tube Amplifier Kit_Analog Metric - DIY Audio Kit Developer20190217_223642.jpg20190217_223701.jpg20190217_223724.jpg20190219_222733.jpg20190219_222742.jpg20190219_222750.jpg20190219_222802.jpg20190219_222837.jpg
 
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MikeyFresh

Moderator
Staff member
Nice, Tony! What is that nice black-jacketed cable you're using for signal?
Mmmm, not Tony here, but I know what that is as I just bought some for an RCA -> 3.5mm interconnect cable build, snazzy Swiss stuff!

Double Reussen shielded design, with two separate counter rotating spiral shields wound at 90 degrees to each other, around a star-quad 24 gauge x4 OFC bundle.
 

airdronian

Junior Member
I've had the idea to try a new brand (to me) of a 6SN7 for the 6BQ5 stereo amp and was snooping for one this morning. Next stop - RCA. (probably)
 

Tleung

Senior Member
I worked on the project last night. My friend also throw me a challenge. He wanted to have two set of output. One for normal amp and one for his powered Subwoofer. I decided not to split the same output to two, instead I have two set of output capacitors. One will be high capacitance and the other will be normal. I found couple of 4uf tub oil cap for the sub out and I will be using a pair of NOS 0.47uf oil cap for normal output. You can see my installation of the 4uf cap in the picture.20190220_220005.jpg20190220_220012.jpg
 

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Tleung

Senior Member
Project is done. Final testing last night. Everything checkout alright just need to add one dropping resistor for filament. Final voltage for filament is around 6.1v. The gain is bit higher than the VTV 6SN7 pre I build both have 1 gain stage but SRPP give out around 17 to 18 times gain. So must use very quiet tubes. I am using a pair of EH tubes for burn in. I will switch to some NOS later. So far I really like the sound of this pre. at initial listening. Very detail and lot of air. I am considering changing the volume control. Currently it is an Alp 24 steps attenuator and I might change it to either more steps or a continuous type.20190221_212621.jpg20190221_232556.jpg20190221_232611.jpg20190221_232617.jpg20190221_232626.jpg
 
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mred

Senior Member
I like the 6sn7 a lot.
I have used them in several amps, one preamp and I even built an active crossover using them once.
When you are ready for tube rolling I can give some tips.
 

mred

Senior Member
Thanks @mred. I am thinking either a pair of sylvania 6SN7GTB chrome top or a pair of RCA 6SN7GT.
Chrome tops are nice tubes, the RCA 6sn7 are not as good.
Tomorrow I will dig out a few nice tube a post up some photos and give you some options. No unubtainium, as I am somewhat frugal.... wink wink , nod nod.
 

airdronian

Junior Member
Chrome tops are nice tubes, the RCA 6sn7 are not as good.
Tomorrow I will dig out a few nice tube a post up some photos and give you some options. No unobtainium, as I am somewhat frugal.... wink wink , nod nod.
Looking forward to that. I can count the 6SN7's I've tried on one hand.
 

mred

Senior Member
Looking forward to that. I can count the 6SN7's I've tried on one hand.
First installment
I like to find bargains so I look for rebranded stuff when seller doesn't know. )
The Tung Sol Micky Mouse ears or round mica relabeled as Remington.
These are my favorite 6SN7, very detailed solid preforming from bass to treble. The top "air " is wonderful.

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Here is the Tung Sol tube
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VT231's the Silvania tubes tend to bring good prices but my in my system these Ken Rad dark VT231 sound better and are cheaper
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Next is a Lafayette branded Tung Sol round plate I would rate this just below the Mickey Mouse ears and about on par with the Ken Rad
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Next a Rathion VT231 another nice tube that should give just a bit more than a chrome top Silvania
20190223_091743.jpg

I will post more later.
 
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Tleung

Senior Member
Well the preamp sound very nice. I ended up using a pair of EH6SN7 very quiet and balance SQ. Only problem I am still be working on the gain is too high. I am asking for some advice. I am thinking of using a Neg. Feedback to reduce the gain but I know very little on Neg. FB. I had been reading online. I came up with the idea of below.

Using a 100K FB resistor from the output (after the output cap) to the front of the input 1K grid stopper resistor am I correct?

Or I can remove the Cathode bypass capacitor but it will change the SQ.

Any suggestions?

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