FU-19 (FM30, 829B) Single-Ended Tube Amp!

nlitworld · « **Reply #240 on:** 12 Nov 2025, 01:33 am »

I'm glad someone finally jumped in with a cap mod. Kinda surprised the cap value change didn't alter the bass response more, but I could see those Jupiter caps really boosting the sound of this kit. Would be interesting a .33uf vs .22uf comparison.

shadowlight · « **Reply #241 on:** 14 Nov 2025, 12:07 am »

My speakers are around 94 db efficient and currently driving it with 2a3 amp.

Jon L · « **Reply #242 on:** 14 Nov 2025, 05:46 pm »

Quote from: shadowlight on 14 Nov 2025, 12:07 am

My speakers are around 94 db efficient and currently driving it with 2a3 amp.

These things also depend on speakers' impedance curve, size of room/distance to listener, size of bass driver, etc. But yeah, I've driven less efficient speakers with 2a3 SET just fine..

FullRangeMan · « **Reply #243 on:** 14 Nov 2025, 07:48 pm »

With a 2A3 tube and 94dB speaker just dont expect this tube last thousands hours.

Jon L · « **Reply #244 on:** 17 Nov 2025, 11:59 pm »

Not having learned to leave well enough alone, I wanted to add a teflon bypass cap, but not having teflon caps in the 1/10th the value range, I ended up adding 1/5th the uF. It still achieved the desired direction of change

nlitworld · « **Reply #245 on:** 18 Nov 2025, 02:59 am »

Lol, just some TFTF Vcaps laying around... no big deal. I bet that really took it up a notch with the cap upgrade!

Jon L · « **Reply #246 on:** 18 Nov 2025, 03:59 am »

Quote from: nlitworld on 18 Nov 2025, 02:59 am

Lol, just some TFTF Vcaps laying around... no big deal. I bet that really took it up a notch with the cap upgrade!

Letting the teflon cap re-burn-in, but definitely more resolution. Some new cables just showed up, too, so those need burn-in as well.

FullRangeMan · « **Reply #247 on:** 18 Nov 2025, 05:21 am »

I really dont understand why you guys remove all these original parts in pérfect working condition and not change these cheap $1 ceramic socket for $30 Teflon sockets that will increase very much the sound quality.

ketchup · « **Reply #248 on:** 3 Dec 2025, 02:30 pm »

Quote from: FullRangeMan on 18 Nov 2025, 05:21 am

I really dont understand why you guys remove all these original parts in pérfect working condition and not change these cheap $1 ceramic socket for $30 Teflon sockets that will increase very much the sound quality.

Do you happen to have a source for Teflon output tube sockets?

ketchup · « **Reply #249 on:** 3 Dec 2025, 02:34 pm »

Quote from: Jon L on 18 Nov 2025, 03:59 am

Letting the teflon cap re-burn-in, but definitely more resolution. Some new cables just showed up, too, so those need burn-in as well.

How are you liking the cap upgrades now?

Jon L · « **Reply #250 on:** 3 Dec 2025, 04:37 pm »

Quote from: ketchup on 3 Dec 2025, 02:34 pm

How are you liking the cap upgrades now?

It's a beautiful thing, almost makes me wish there was equal hype around FM30 tubes when 300B/2A3/45 tubes were getting all the audiophile attention, ending up with a lot of my money..

ketchup · « **Reply #251 on:** 8 Dec 2025, 05:17 pm »

Are you guys using these with a preamp or not? What are your experiences with and without a preamp?

FullRangeMan · « **Reply #252 on:** 8 Dec 2025, 08:09 pm »

Quote from: ketchup on 3 Dec 2025, 02:30 pm

Do you happen to have a source for Teflon output tube sockets?

I will see it tonight when I arrive at the desktop.

FullRangeMan · « **Reply #253 on:** 8 Dec 2025, 10:53 pm »

Quote from: ketchup on 3 Dec 2025, 02:30 pm

Do you happen to have a source for Teflon output tube sockets?

Sorry to have not see your post before.
First let me say that Ceramic Tube Sockets are the worse sockets one can use,
its sound are awful, they are very microphonic, they transmit vibration from the
transformers to the tubes as a bell, the ceramic is a hard material that does not
react with heat like Teflon. Its vantage are they are cheap and last until the rivets
on the ceramic contacts loosen.

I get mine years ago from Jake in Italy.
https://www.jakeband.it/contatti-contact.html
You must ask to Septar Sockets usually used in 6C33 tubes.

At those times Septar Teflon sockets was available only from some
audiophile sources as PCX, Yamamoto, Good Component etc...
Today Teflon Sockets are much more rare, but you could try here:
https://www.bartola.co.uk/valves/2016/03/20/teflon-sockets/

FullRangeMan · « **Reply #254 on:** 8 Dec 2025, 11:24 pm »

As a second alternative there is the Russian Rubberized Bakelite
Model PL3-1pD37 made by Silbelkom.
They are cheap, small and will last a century.
I happen to have some spare if GSTube.com dont have any to sell you.
https://www.gstube.com/catalog/rsh3-0/

FullRangeMan · « **Reply #255 on:** 9 Dec 2025, 01:36 am »

Other miscelaneous Sockets of interest:
PLK7 Collect Ceramic Russian Military Missile Socket for 6C33:

Ceramic Socket for GK71 Pentode:

PCX Teflon Septar for 6C33:

Russian Rubberized Bakelite:

ketchup · « **Reply #256 on:** **Yesterday** at 02:29 pm »

I just got one of these amps and it arrived in perfect condition. Its appearance is nearly flawless. Mine came with a Russian input tube.

mick wolfe · « **Reply #257 on:** **Yesterday** at 05:27 pm »

Quote from: ketchup on 8 Dec 2025, 05:17 pm

Are you guys using these with a preamp or not? What are your experiences with and without a preamp?

I realize this is going to depend on one's system, but I preferred it solo with no pre-amp in front. That's probably why it now resides in my bedroom system streaming Spotify into Klipsch 600M's. When I used it with a Schiit Freya+, ( FU-19 volume pot wide open ) it sounded a bit congested by comparison. So could be no more than a component mismatch on my end, but for now it will continue to do its work solo.

Jon L · « **Reply #258 on:** **Yesterday** at 06:30 pm »

Quote from: ketchup on Yesterday at 02:29 pm

I just got one of these amps and it arrived in perfect condition. Its appearance is nearly flawless. Mine came with a Russian input tube.

Interesting. That's the Voskhod 6N2P (non-EV). Maybe they ran out of the chinese 6N2 stock. What output tubes did it ship with? I kind of like the sonic signature of Chinese 6N2 driving Chinese FM30 output tubes actually..

ketchup · « **Reply #259 on:** **Today** at 12:49 am »

Quote from: Jon L on Yesterday at 06:30 pm

Interesting. That's the Voskhod 6N2P (non-EV). Maybe they ran out of the chinese 6N2 stock. What output tubes did it ship with? I kind of like the sonic signature of Chinese 6N2 driving Chinese FM30 output tubes actually..

It came with the Chinese FM30s. I have some NOS 1944 National Union 829B JANs and NOS 1988 Cetron 3E29 JANs to try.