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Any Fi X3 300B amp owners out there?

Orest12 said:
The amp was shipped in 99 with period EH 300b, average quality, two JAN Phillips 6sn7, and a Sovtek rectifier, which arced in a week. I replaced it with an old Dynaco branded Mullard harvested from a ST70, still testing and sounding as new nearly 60 years later. 300b using: 90’s Svetlana (sounds great), Sovtek (like the EH), Audio Note branded Shuguang black plate (sounds great). Also used briefly Western Electric reissue but the tube manual advises to use this tube vertically if possible. For the driver tubes I recently tried a pair of Psvane Treasure II, the big gray bottles. These are very microphonic in a Cary preamp, but are quiet and play well in the X—no idea why.
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Good to know. This X3 still has the Sovtek and US-made Sylvania 6sn7 GTBs it likely was delivered with by Garber, but the 300Bs have been rolled. I'm headed to my dealer's place this afternoon with the amp for a tube rolling session to rule out noise from bad/weak tubes. Once fresh tubes are in, I'll have a much better idea for how much of a refresh I'm in for. Fingers crossed...

As for tubes, I'm really hoping the GTBs are still solid. For the rectifier, Sovteks are solid tubes but not my favorite, so all bets are off. Mullards are my happy place for the 12ax7 and 12au7. I salvaged a couple of grey-plate 12ax7 Mullards, that were made in the Blackburn factory, out of an old el84 push-pull integrated from the 50s, and they immediately turned me into a Mullard junkie. For the 300B, if they need to be replaced, I'll likely start with JJ and go from there. I'm running JJ 2A3-40s in my Asano amp, and they easily throw down with the NOS RCA-2A3s I also have. In fact, I prefer the JJ to the RCA.
 
A few more thoughts--In the past several months I have used the amp more than in the first 18 years. Two things have changed my thinking and preference. First I teamed it with a solid state preamp (Mc C712) rather than my Cary tube; also am using Psvane Treasure drivers which don't work well in a preamp (microphonic) but are amazingly good in the X. Somehow the thing seems much more dynamic and powerful and is great fun to use.
For general interest: two Fi X 2a3 amps were on eBay lately. In February one described as a Magnequest/Cerafine amp sold for an astounding $2827; about three weeks ago an amp described as standard did not make reserve at $1550.
 
Orest12 said:
A few more thoughts--In the past several months I have used the amp more than in the first 18 years. Two things have changed my thinking and preference. First I teamed it with a solid state preamp (Mc C712) rather than my Cary tube; also am using Psvane Treasure drivers which don't work well in a preamp (microphonic) but are amazingly good in the X. Somehow the thing seems much more dynamic and powerful and is great fun to use.
For general interest: two Fi X 2a3 amps were on eBay lately. In February one described as a Magnequest/Cerafine amp sold for an astounding $2827; about three weeks ago an amp described as standard did not make reserve at $1550.
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By the time Garber passed, he had a 3yr waiting list and was declining new commissions. (I spent the last month or so he was alive sweet-talking him to add just one more name.) For those of us who were too late to the party, I can understand why some are willing to pay a premium. My X3 was still acquired for under the final list price Don was handing out, but he was mostly known for his 2A3 designs, which may be why the optioned X 2A3 was able to command a premium.

As for those Psvane drivers, are they quieter than the others, or just giving better performance?
 
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Those Psvane drivers are a bit of a fun puzzle—microphonic in a preamp, but dead quite and sonically great in the X, best of several drivers tried over the years including the famous red base rca tubes. After
swearing at them for about two years, I’m glad to have them now. Will try another one in my audio note kit one.

Also, will be picking up a dealer demo Heresy iii today for a 30 day trial; always wanted a horn and will advise how it goes.
 
Orest12 said:
Those Psvane drivers are a bit of a fun puzzle—microphonic in a preamp, but dead quite and sonically great in the X, best of several drivers tried over the years including the famous red base rca tubes. After
swearing at them for about two years, I’m glad to have them now. Will try another one in my audio note kit one.

Also, will be picking up a dealer demo Heresy iii today for a 30 day trial; always wanted a horn and will advise how it goes.
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Good to know on the Psvanes. I'm definitely a believer that quality drivers are every bit as important as the output tubes and rectifiers. I had the amp checked out at my local dealers and 80% of the noise/hum issue was coming from the Sylvania GTB drivers. In fact, one of them gave up the ghost while we were troubleshooting. We plugged in a couple of replacement drivers that were yanked out of a Line Magnetic, as well as a Mullard rectifier, and the X3's output quality was night and day.

And let me know how it goes with those Heresy IIIs. The earlier alnico-based version of that family of speakers is on the the shortlist for matching the X3 to use in the studio.
 
Great match—Fi X and Heresy horn. If that first watt philosophy/cliche means anything this speaker will not use half of that first watt. It’s great fun to listen to and that is all I want from this hobby. But, that hum designed into the amp, fairly well masked by “normal” speakers is quite noticeable.
 
Orest12 said:
Great match—Fi X and Heresy horn. If that first watt philosophy/cliche means anything this speaker will not use half of that first watt. It’s great fun to listen to and that is all I want from this hobby. But, that hum designed into the amp, fairly well masked by “normal” speakers is quite noticeable.
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So it's not the Hammonds or the Elna Cerafine causing it... Good to now.
 
Hi Grantray,

How and when did you get Isamu Asano amps??

I never knew these were made, I thought Asano was only a DIYer who had his circuit published, prior to Shishido's DC amp??

The Fi schematic posted in this thread shows no Hum Pot, yet you mention a Hum Pot, in two of your thread's posts.

Are you sure you have a Hum Pot in your amp?? If so, please allow me to mention something .......for you to consider.

Most DHT tubes using hum pots ( only ) have a ( fixable ) weakness in their design.

The interface between the pot's center wiper, and the pot's internal resistive element, acts somewhat like a diode, it partially rectifies the JJ 2A3-40 or 300B's cathode's audio signal, in the tube's return-to-ground path.

Designers / DIYers / people who are aware of this, simply add a SOLDERED pair of resistors, from each end of the pot, to the center ( wiper terminal ).

A typical resistor value may be 15 to 25 Ohms , 2 Watt, high-quality would be preferred.

This does several things, the most notable IMHO, is that you have changed the return to ground from a " diode - like / rectifier - like " wiper-interface, to a added - SOLDERED current - return - path, to ground.

Most who do this, report an improved sonic result, and your large / beefy JJ 2A3-40 or a 300B would benefit from such a soldered connection IMHO. Please look this up, on line.

I personally am a big fan of the two stage DC SET circuits, as you seem to be. Less becomes more. I have written a 32 page paper, tracing the history, and implementations of this specific amp type, ( from 1929 to 2018 ) and would be happy to email it to you, if you would like to read it.

I drew out a diagram, below, of where to add the resistors. Also, I can mail you (4) 15 Ohm, 2 Watt Cornings, for the cost of postage, if you would like to hear this.

Good listening to you !! I DIY build these amps from scratch, just for myself ( use ALTEC VOTT A7-800s ) and have done so, past 12 years.

Dowto1000

.Rs across HUM POT.JPG
 
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Jeff is correct that even some commercial amplifiers fail to properly implement the hum pot. Without the two resistors bypassing the two legs of the hum pot, all the current for the output tube, generally 60mA or so, goes through the wiper of the pot! This creates considerable noise and hum and as time progresses the pot gets even noisier. This situation is easily remedied as he has pointed out with 15r to 20r resistors that take most of the current flow. I consider this a mandatory implementation for any DHT with a hum pot and cathode resistor.

SE hum pot.jpg
 
Appreciate reading the last two posts from Palustris and dowto1000 –thanks much for the advice. The X3 does have a hum pot, at least the one I have bought from Don Garber over the phone 19 years ago. The X amps were built as economy units, and as Garber mentioned kindly, live with the hum or return the amp. In my amp the pot really has very little or no effect, but I will solder in the resistors and hope it can easily be done because of the unique design.
 
Orest12 said:
Appreciate reading the last two posts from Palustris and dowto1000 –thanks much for the advice. The X3 does have a hum pot, at least the one I have bought from Don Garber over the phone 19 years ago. The X amps were built as economy units, and as Garber mentioned kindly, live with the hum or return the amp. In my amp the pot really has very little or no effect, but I will solder in the resistors and hope it can easily be done because of the unique design.
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SO, on efficient speakers, you have some hum with the Fi X. ??

Can you hear it with the amp at idle, at your listening position ?? If not, don't sweat it .....at all.

What does it measure ( mVAC ) amp at idle, with what kind of meter, at the amp's output terminals??

The hum pot's winding-wiper interface MAY be causing some of the sonic degradation you are hearing, as the unsoldered wiper " rectifies" the cathode's return to ground .

The added 15 Ohm Rs we suggested in this thread are needed IF your amp uses any Rk hum pot, IMHO.

( I hate hum pots, will never use them in my own 2A3 DC SET builds. )

I put up with some hum, ( on efficient well-wired ALTEC VOTTs ), but I feel I get a better overall result, feeding the 2A3's cathode resistor directly from the center tap of a Hammond 2.5 VCT Ef XFR, no pot. It is my own DIY 2A3 amp build preference.

Please, by all means, especially to help other Forum Members, DO let us know, what you hear, after soldering these 2 Rs on each pot !!!

eBay search words : " 15 Ohm 2 Watt, Cornings, or CGW " which will get you 50 pieces for $8.15, a bargain for that quality of an R. NO crummy carbon comps please !! Also, a high quality Roederstein MK-8 2 Watt R will do swell - $$$$ at Percy.

Dowrto1000
 
Thank you again, the X3 hum does not discriminate—it hums on all speakers. Never bothered me much, no sweat as you would say. I am most anxious to add the resistors as you advise. Actually before reading you latest post, I already checked on a supply source. That’s the easy part—how to get at the pot is the problem because of the odd ball design. Some panels need to be removed with heavy parts attached, etc. and then put back; doesn’t look easy, at least not to me. Speaking of odd ball, I looked inside the amp between two ot the panels for the time ever after your post. I see in there tangled with the wires a big pierce of paper: Don Garber’s humor, hidden message, or just a case of the sponge left inside? Will be glad to keep all those interested posted, if I can do the recommended job.
 
It is possible that the paper has the schematic on it. Also there is probably an easy way to open the amp properly. Don't forget that Don had to build and maintain the amps, so there is probably a systematic way to open them up. See the second paragraph in the letter on post 11.
 
Restistors ordered and coming tomorrow. Also, might have figured out how to reach the hum pot. The X has four right angled panels. The one housing the tubes must come off—14 fasteners and screws hold this panel on. Regarding the paper inside, hope it’s the schematic; what a creative way to include it. Keep you informed.
Also, if the hum pot is so undesirable and doesn’t really do anything, could it be removed, and how?
 
What brand and construction of resistors ??

Yes, a hum pot can be removed IMHO, and it usually sounds better, at least in my DIY builds, overall.

In an Fi amp like yours, proceed conservatively. Try the added Rs and hear that first, to learn, gain experience. No one will be able to easily tell if you added them in there :).

After doing that, you alone will be able to best decide, if you want to physically leave the pot intact, and just not connect to it. But, try the added Rs - and hear that first.


The LESS parts you have as the SET's signal path, ( and the better the parts and lay out ) - the better a SET amp should sound.

To me, that is "THE" compelling reason to go only two triode stages and directly coupled !!!!!

( Most recent USA commercial SET offerings are / or were AFAICT : Fi, Moth, Serious Stereo ) Any others??


" Less parts " applies to totally eliminating hum pots and grid stopper resistors, IMHO. As a DIYer, I also short-out my amps' current inrush device ( CL-90 thermistor ) and 120 VAC line-fuse, after start up, in what I term any " attended listening " session.

RE : " No hum pot " : please see 2/3rds down in my post #32, and, also the Fi 2A3 schematic posted in this thread, post #11.

To implement no hum pot, you just connect the Center Tap of a Hammond 2.5 VCT at 3A. filament transformer, to the top of your cathode resistor, to self-bias the tube. Other end of Rk goes to ground. Use shortest possible ( heavy, high quality ) wire paths in the Rk return circuit of the 2A3, to star ground The body length of the Rk resistor should make-up much of the distance.

For lay out, I like to position my DHT Ef XFR at least four inches away from the 2A3 tube socket and pins, so the Ef XFR's magnetic fields interact less with the circuit.

I routinely replace all the stock leads, in and out of the Hammond Ef XFR ( and Power Transformer, and lower DCR Hammond Chokes) , with high-quality, wide bandwidth wiring, m22759/11.... 14 AWG, etc.

These build techniques sonically gives the 2A3 amp higher dynamic contrasting and a wider bandwidth. All these techniques are audible to me, and cumulative.

And, when wiring my amps, my preferred style of DIY DHT amps sound better to me, if the Ef XFR leads are NOT twisted,..... the 120 VAC primary, and the 2.5 VCT secondary leads' wiring !! John Swenson E.E. wrote about this - referring to the High Voltage Power Transformer secondaries, long ago, on A.A.

YMMV, but I am having a lot of fun, and its exciting.

Dowto1000
 
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dowto1000 said:
" Less [sic] parts " applies to totally eliminating hum pots and grid stopper resistors, IMHO. As a DIYer, I also short-out my amps' current inrush device ( CL-90 thermistor ) and 120 VAC line-fuse, after start up, in what I term any " attended listening " session.
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Well, Jeff, these ideas are all possible avenues of exploration for the advanced builder with technical knowledge willing to invest the time. However I think it is inappropriate to lay out these ideas as a kind of blueprint to good sound. For instance, removing grid stoppers with high transconductance tubes will lead to the tube oscillating and possibly at a frequency not visible on the average hobbyist oscilloscope. Using the D3a, E180F and 7788, I found it necessary to not only use grid stopper resistors, but I had to put ferrite beads on the heater pins. So, my point is that for the average hobbyist grid stoppers, hum pots, fuses and such are all necessary components to ensure best and safest performance from his amplifier and the elimination of these is generally not warranted.
 
I understand where you come from. No problem .

I usually don't use high transconductance driver tubes.

The Fi input tube is low transconductance.

I was referring to my own SET implementations and experiences in my posting, and really not the average person's builds.

Instead of ferrite beads Palustris, I do use hash chokes, on the heater pins of my amps' driver tubes, at the socket, on every build.

Dowto1000
 
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