FX Audio 6j1 tube preamp - a $31 wonder

pio,
i can't answer if 15v would be too much for the pre to handle, but i'd measure the power supply voltage before i'd try it if i was feeling adventurous
the pre is really inexpensive so maybe the heaters would burn up? if you have some extra tubes, or the original inexpensive tubes & you think you'd like to experiment with tube rolling, i'd say go for it as probably only the tubes would be damaged?
it it doesn't immediately fail, maybe the life of the tubes would be shortened, but it might sound better?
would the operating point of the tube change with a higher voltage to the plate? maybe someone with a handle on tube amp design can chime in :)
The internal power unit may have a regulation feature that keeps B+ constant over a range of input, the heaters likely would not, and higher than normal heater voltage giving hotter than normal cathode, increasing electron emission, would be somewhat equivalent to running higher B+. This would definitely affect the operating points, it probably wouldn't increase peak output level as increasing B+ may.
Otherwise, if the B+ were to also increase, then the effect with the hotter cathodes on the operating points would be greater still. Observational effects vs measurements of this abnormal state might be useful for curiosity sake, intentional design is always better.
 
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When I buy Russian tubes I often go with the ev designation which identifies them as military spec tubes. Not that they sound better but are more robust and designed for use in the field. Russian MIG fighters used ev tubes in their avionics. In this case they would be 6j1p-ev.
 
When I buy Russian tubes I often go with the ev designation which identifies them as military spec tubes. Not that they sound better but are more robust and designed for use in the field. Russian MIG fighters used ev tubes in their avionics. In this case they would be 6j1p-ev.

Would you consider this FX unit to be an upgrade over the Sainsmart, or on the same level?
 
Hi, I've been following the TPA v tripath thread for years and have had three of those off-the-shelf amps now (SMSL 36a PRO, SMSL SA60, FX502SPRO) and am very impressed with them.

I also just caved and bought one of these tube buffers, got it for a discount price of £19 on Amazon, so it was impossible to resist!

Thinking about inexpensive upgrades to the stock tubes (about which I know nothing at all) and saw these Voskhods going cheap. What is likely to be wrong with them at this price, or should they be just fine?! I notice they are not matched or individually boxed, nor do they have the EV designation, though the ad does say they are NOS military stock...

https://www.ebay.co.uk/itm/6-x-6ZH1...197668?hash=item260a0a3264:g:uwwAAOSwfX9b7rLN
 
Both of my much loved 6n3 tube preamps are now in storage. The FX with it's superior potentiometer powered by the linear psu is a step up.

Those Russian tubes linked above are excellent choices. Unlike the US which got rid of all their tube tooling the Russians kept theirs. But don't discount the stock Chinese tubes which happen to sound very good. That's not the case with most of the tubes that come with gear exported from China.

Matched tubes are not a big deal.
 
Hi, I've been following the TPA v tripath thread for years and have had three of those off-the-shelf amps now (SMSL 36a PRO, SMSL SA60, FX502SPRO) and am very impressed with them.

I also just caved and bought one of these tube buffers, got it for a discount price of £19 on Amazon, so it was impossible to resist!

Thinking about inexpensive upgrades to the stock tubes (about which I know nothing at all) and saw these Voskhods going cheap. What is likely to be wrong with them at this price, or should they be just fine?! I notice they are not matched or individually boxed, nor do they have the EV designation, though the ad does say they are NOS military stock...

https://www.ebay.co.uk/itm/6-x-6ZH1...197668?hash=item260a0a3264:g:uwwAAOSwfX9b7rLN

And welcome to AK my friend.
 
And welcome to AK my friend.

Thanks :)

I already bought those Vokshods, they should arrive by the Spring, or shortly thereafter :)

I did see that you and others rated the Shuguang (?) tubes as decent, but at that price I thought I would give them a go, out of curiosity mainly.

But got to get my amp fixed before I can do any critical listening of the FX 01 :(
 
Both of my much loved 6n3 tube preamps are now in storage. The FX with it's superior potentiometer powered by the linear psu is a step up.

Those Russian tubes linked above are excellent choices. Unlike the US which got rid of all their tube tooling the Russians kept theirs. But don't discount the stock Chinese tubes which happen to sound very good. That's not the case with most of the tubes that come with gear exported from China.

Matched tubes are not a big deal.
The Chinese 6N3 tubes could be military production line stock, possibly Russian design from Russian sourced line fabrication gear. There is otherwise no market or demand other than these little oddball line stages, afaik, and no economic reason to tool up a production line for them.
 
When I buy Russian tubes I often go with the ev designation which identifies them as military spec tubes. Not that they sound better but are more robust and designed for use in the field. Russian MIG fighters used ev tubes in their avionics. In this case they would be 6j1p-ev.


Do you think they sound better than the equivalent U.S. built aircraft?
 
Do you think they sound better than the equivalent U.S. built aircraft?

Hard to beat the tube warmth of this puppy especially when the afterburners kick in. :D

mig-29s.jpg
 
The Chinese 6N3 tubes could be military production line stock, possibly Russian design from Russian sourced line fabrication gear. There is otherwise no market or demand other than these little oddball line stages, afaik, and no economic reason to tool up a production line for them.

Not an oddball line stage at all. Excellent equivalents for the Chinese 6n3 include Russian 6n3p-ev, 5670 and the highly coveted WE396A and 2C51. The WE's often sell for $100 each. I had a quad in my Dared and when one popped I was depressed for a week.
 
Not an oddball line stage at all. Excellent equivalents for the Chinese 6n3 include Russian 6n3p-ev, 5670 and the highly coveted WE396A and 2C51. The WE's often sell for $100 each. I had a quad in my Dared and when one popped I was depressed for a week.
Oddball in the sense of using a tube that was originally a milspec RF pentode as an audio small signal triode. I don't recall any consumer gear using 6AK5 for anything before these Chi-Fi line stages.
 
Oddball in the sense of using a tube that was originally a milspec RF pentode as an audio small signal triode. I don't recall any consumer gear using 6AK5 for anything before these Chi-Fi line stages.

Odd to you maybe. What tubes were originally designed for has little to do with their current audio application.
 
They were once cheap and plentiful because they didn't have consumer application. Dunno how many probably went to landfills due to no demand. I had a grunch of them hand-me-down milsurp with no use when I was a kid.
Marantz repurposed a 6BH6 linear RF pentode like this as a triode in the front end of models 5 and 8/8B in the latter 1950s.
 
They were once cheap and plentiful because they didn't have consumer application. Dunno how many probably went to landfills due to no demand. I had a grunch of them hand-me-down milsurp with no use when I was a kid.
Marantz repurposed a 6BH6 linear RF pentode like this as a triode in the front end of models 5 and 8/8B in the latter 1950s.

The Russians cloned the 2C51/5670 and called it the 6N3p. The Chinese cloned the Russian 6N3p and called it the 6N3. Don't know if I can link this but it's a history of 5670. It's well regarded, in demand, and certainly not meant for a landfill.

https://www.audiocircle.com/index.php?topic=148150.0
 
The Russians cloned the 2C51/5670 and called it the 6N3p. The Chinese cloned the Russian 6N3p and called it the 6N3. Don't know if I can link this but it's a history of 5670. It's well regarded, in demand, and certainly not meant for a landfill.

https://www.audiocircle.com/index.php?topic=148150.0
Those aren't 6AK5, they are small signal twin triodes.
I do not not know when hobbyists adopted either.
Certainly not dump fodder now, my 6AK5s (lost in storage and probably trashed) were acquired in the 1950s as hand-me-down milsurp, and afaik were mainly used in radar IF strips.
 
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