[floobydust]

 After a bit of a hiatus from actually designing and building gear I got back into things about 18 months ago. Some time was spent looking at what was available in parts... mostly transformers. I wanted to build something basic up first that was more of a tried and true design and found the Shishido RW 2A3 SE schematic. It used Tango iron in a simple direct-coupled design which seemed reasonable. I opted to use some parts I had on hand which included some NOS Triad units (Power xfrmr and Choke) and some NOS die-cast alloy boxes... (aka ugly enclosures). I required some decent output transformers and purchased a pair of RH40s from Mike at Magnequest (really nice guy). I changed the circuitry around a bit... dumped the paralleled 12AX7 dual-triode for a 6FS5GT and opted to use a pair of 45 triodes, made the appropriate circuit value changes and split the hum balance so I had separate AC and DC adjustments. I did use basic parts in all but opted for Caddock resistors in the actual circuit as their aren't that many of them. These have worked out well overall and sound quite nice. They were built into 3 chassis: one common power supply and two separate amp chassis with 8 conductor umbilical cords to the power supply.




 After this I got serious and spent many months on a clean sheet design. I also found Hashimoto transformers and after swapping some emails with Isao bought some of these gorgeous units... probably some of the best built transformers around and very attractively packaged. To use these properly I designed a 3-stage circuit consisting of an input amp direct-coupled to a driver stage with capacitive coupling to the output stage. From a design standpoint, I don't believe in tubes like the 6DJ8 (great in intended-use, which was NOT audio), nor do I care for any current-sourced stuff like SRPP.. tried that back in the 80's... and left it there! Tubes I actually will use include the 12AX7, 12AU7, 12AY7 and 6FQ7 along with commerical versions which include 5751, 5814, 6072. Oddly, the 12AT7 is great tube but have not needed it to date. Anyway.... I digress. Parts selection was also critical and I opted for a combination of Caddock and Mills resistors and used Axon caps for all filter/resevoir, bypass and coupling. Pure silver wire was used for anything critical and this added up to a parts cost of pver $1100 per chassis! The end result is excellent (IMnsHO). I posted these pics on some other audiocircle forums a while back but opted to post again.




 Finally I decided to build up a inexpensive SD speaker and used the Fostex FX120 in a very simple ported enclosure based on their recommended design but used Blackhole products for damping inside. These were done quickly using sand-ply and MDF from Home Depot and cut on my 40+ year old radial-arm saw (okay, I bought a new blade). I put a commercial-grade 1/4-inch cork on the front to hide the plywood egde and they worked out quite well for the price. They also sound really good (on good stands) which has left a very good impression of Fostex with me.




 So... next on the list... similar amps to the Hashimoto based ones above but using RCA-Cunningham Single-Plate 2A3 with the appropriate circuit changes (more than most would think) and a new enclosure design using the Fostex F120A and augmenting it's high-frequency response with a Fostex T90A crossed over at 6dB/octave at ~15KHz. Hoping to have these done by end of the year... then move into the 20-watt Hashimoto iron and a WE300B output tube. Sorry for the long post and the big pics... hope all enjoy.

 Regards, KM
 

[jrebman]

KM,

Very nice -- just wish I could see the pix.  Sounds like a couple of great projects.

How are they (the amps) sounding?

Thanks for posting this.

-- Jim

[floobydust]

 Jim,

 I'm assuming you have a problem for not being able to see the pics (too bad). As for the sound of the Hashimoto based amps, they are really quite exceptional. Using good quality tubes is critical of course but I've used them to drive the Quads (low sensitivity) and they are excellent is every regard... I'll avoid the usual audiophile accolades but they are very special. I consider signal-to-noise to be a critical factor which affects everything... and most people, for some odd reason, accept noisy amplifiers, especially in SET designs, yet rave about the sonics once you crank the signal above the noise. These amps exhibit s/n ratios which are perfectly acceptable with the highest sensitivity speakers. With good tubes they have an output noise below 150 microvolts. Measured specs using NOS tubes were:

All measurements done at 1-watt into 8 ohms (2.83VRMS)
 Output: rated 2-watts, clipping at 2.25 watts
 Frequency response: 25Hz - 45KHz within 1dB
 Output noise: below 150 microvolts (8 ohms)
 Signal-to-Noise (measured) ~85 dB below 1-watt
 Distortion: <0.5% at 1-watt, 1.5% at 2.0 watts maximum

 Of course specs don't mean everything, and I've used some tubes that are not that great... but I do have a very large collection of 45 triodes to pick from (lucky guy am I). I have Ken-Rad, GE, Philco, Sylvania (green print and engraved base), RCA (both ST and balloon) and Tung-Sol ... in some cases multiple pairs of each. I still love the 45 overall, probably my favorite of all the old DHTs. Once the 2A3 versions are completed I'll be able to test my large collection of those as well.

 Regards, KM

[jrebman]

KM,

I know you probably don't know this, but I happen to be blind, so that's why I can't see the pix -- not a technical issue.

Sounds like a pretty great tube collection there.  Right now I'm more in the EL84 camp with my most recent acquisition being a NIB NOS pair of Siemens Halske e84ls, matched, premium grade and with Munich factory production codes.  I'll probably have to wait until sometime next year to hear them though as I'm in line to get a Vaughn Carina amp.  Already have the NOS Mullard rectifiers, now got keep my eyes out for some nice 7308pqs and other 6DJ8 flavors.

-I know what you mean about being sensitive to SNR -- that may be why I've not considered buying any of the 2A3 amps I've heard -- very nice, classic tone, but never heard one that wasn't audibly noisy.  That doesn't mean they don't exist, just that I've never heard one myself.

-- Jim

[floobydust]

 Jim,

 Now that I have my foot out of my mouth (sorry)... my very first amplifier had an EL84 in it... my Dad built it for me when I was 7 years old. Great little SE amp with a 6AU6 driver and a 6CW4 rectifier. Siemens-Halske made superb tubes over the years, especially their EL34s. Years ago I had a pretty good number of Amperex Bugle-Boy 6DJ8 tubes... I actually gave them away to a guy that used them... can't even recall what he used them in actually.

 I've had varying luck with 2A3 tubes... as the double-plate versions are actually two triodes paralleled in the same envelope. These are difficult to get the hum out but I do have some RCA black plates and gray plates that are very quiet. The 6A3 (and 6B4G) are impossible to balance the hum out as they wire the two filaments in series rather than parallel... I finally resorted to a DC filament for those but eventually abandoned them altogether for the 2A3.

 I'll have to check my stash to see if I have any 6DJ8 tubes left... will let you know. I would also look for some of the non-mullard GZ34/5AR4 rectifiers that used copper-lined plates. GE made some and they are quite good... and you don't pay the extreme prices for them either. I recently gave my brother a pair of these that were GE-made and Westinghouse labeled/boxed... he's a happy camper, I might have one left.

 The Carina gets great reviews from owners... hope you get one soon.

 Regards, KM

[jrebman]

KM,

Thanks, and if you have any 6dj8s that you'd be willing to part with, just PM me with details.

I've recommended the GE 5AR4s as well, just don't have any at the moment, but since I've had a pair of these Mullards, why not use them?   Eddie Vaughn likes the new JJs as well and says they are close to the Mullards, just don't last nearly as long.  In fact, I've heard of people needing to replace their modern 5AR4s, especially Sovteks, every year -- so $20 bucks a year, or $120 for 20 years or more?  Sounds like a no-brainer to me .

Someday I may get around to designing and building a PSE 12B4A amp with 3 or 4 tubes per side -- there are zillions of them around, sound pretty nice, and are cheap.  Sort of along the same lines as one of the E.A.R. amps that use 10 12ax7s per channel -- I wouldn't want to retube that one with NOS tubes.

Anyway, today I'm going to send an email to the guy who built my speakers to see what he thinks of using the FX-120 in them.



Thanks again,

Jim

[DaveC113]

Hi FD,

It looks like you have covered the front of your cabinet with felt. I was considering doing that using 1/8" thick high density pure wool felt. Do you have any comments or advise on doing this?

Good job on the amp, too! 

Thanks,
Dave

[floobydust]

Hi FD,

It looks like you have covered the front of your cabinet with felt. I was considering doing that using 1/8" thick high density pure wool felt. Do you have any comments or advise on doing this?

Good job on the amp, too! 

Thanks,
Dave

 Not sure who FD is, but if the response was about the FX120 ported cabinet pics above, the fronts are covered in 1/4-inch thick cork. I found this on the net from www.bangorcork.com in 4-foot wide rolls sold by the foot and available in many colors. It has (had) a burlap backing which I stripped off and sanded smooth before using a spray adhesive to attach to the front. It's pretty dense for cork but has a nice texture, consistent color and thickness and can be sanded easily. It smells funny however.

 The reasons for using this was two-fold: first, cosmetic... covering the front edges of the plywood and the MDF front baffle board and two, provide a surface that is not so hard acoustically. Overall it worked out well and is just the right thickness to make the driver look flush.

 Thanks for the kudos on the amp... they were mechanically done using AutoCad and 1:1 scale templates were plotted which I taped to the chassis for marking, etc.

 Regards, KM

[DaveC113]

 Not sure who FD is,

FloobyDust   

Thanks for the info... I think the felt will serve a similar purpose as far as having a not-so-hard surface for sound to reflect off of. I'm skeptical that it will do much good because the 4.5" driver seems to have a more directional radiation pattern than a typical dome tweeter...

Dave

[floobydust]

 Not sure who FD is,

FloobyDust   

Thanks for the info... I think the felt will serve a similar purpose as far as having a not-so-hard surface for sound to reflect off of. I'm skeptical that it will do much good because the 4.5" driver seems to have a more directional radiation pattern than a typical dome tweeter...

Dave

 I feel like Homer.. Doh! 

 Regards, KM