My low watts projects

[Ty_Bower]

My listening room. Hornes with Fostex FE 206E

Nice horns.

[azazello]

Next my two stages ampl. SE JJ 300B & 6E5P & OT Hammond 125 FSE - 90 ma, chase Hammond.
Two electr. chock filtering, fixed bias, caps - Auricap, ELNA Cerafine, Phillps, Rubycon.

http://picasaweb.google.com/azazello52/ ... 4050970514
http://picasaweb.google.com/azazello52/ ... 2897531442

I changed electr. chock to iron, because I founded that el. chock doesn't avoid big moment energy cross to the amplifier.
It was second try and I decided never use el. chock!
I increased every plate current to 90 ma /more current - big sound!/, and I changed interstage caps to russian ФТ-3 - 0,47 uF and result is very, very fascinate and amazing! ФТ-3 is my favorite!
Uplate = 352 v, fixed bias -65v. For prestage 6E5P - U plate = 190 v, Iplate = 25 ma, Rplate = 7 kohm, R cathode = 100 ohms. U cathode = 2,5 v.. Cathode shunt ELNA Cerafine - 1000 uF /only 8 passive elements per channel!/.

[EWBrown]

I finally got an opportunity to view all 128 of your DIY amplifier photos, all are very nice! I have a slow speed internet connexion at home, and here I have 100MB/s so it doesn't take long to for a photo to download.

/ed B in NC at the soundboard (and this is a really easy one for me to run)

[Geek]

I have a slow speed internet connexion at home....

Isn't your day job running an ISP or something?

Cheers!

[EWBrown]

My day job is being retired ;-) The soundboard ops are just for fun.
Besides, I always have the best seat in the house

/ed B Truly havin' a Great Day ! (Yeah, I'm running the sond for a gospel music group named "Great Day" from Florida).

[azazello]

Thanks EWBrown!
Now I work on project SE exotic voice 4P1L & PCC88-Siemens & Hammond 125FSE.
I will post a photo later. I use fixed bias, Uplate = 150 v, I= 50 ma, -U=6v, DC heating=4v.....only 1 passive element /grid res./ in output stage!

[soundbrigade]

Azazello is on his way to Sweden to take active part ( ) in the yearly DIY meeting in Gothenburg 14th of May.
We will make sure that Azazello is taken care of during his stay here and I hope he won't mind finishing my many projects that are lying around.

Btw. found parts to an almost finsihed PP-amp for EL84 in the basement ...

[azazello]

Azazello is on his way to Sweden to take active part ( ) in the yearly DIY meeting in Gothenburg 14th of May.
We will make sure that Azazello is taken care of during his stay here and I hope he won't mind finishing my many projects that are lying around.

Btw. found parts to an almost finsihed PP-amp for EL84 in the basement ...

OK! Good idea, but I have a little bit time to finish Your started projects.....

[azazello]

https://picasaweb.google.com/azazello52 ... 2947255474
Mi finished project SE exotic tubes 4P1L & PCC88 Siemens, I will bring with me for DIY Expo in Goteborg.....U plate-cathode PCC88 = 130v, Ia = 5,4 ma, Cathode shunt "Panasonic" with very clear sounding. Interstage caps K40-Y9 or ФТ-3, I will listening some days and will decide. Output tranies -
big excellence Hammonds 125FSE. Output power is 1.5 Watts per channel /triod mode/, but sounding is like 2A3

[azazello]

https://picasaweb.google.com/azazello52/Amplifiers#5594368832947255474
Mi finished project SE exotic tubes 4P1L & PCC88 Siemens, I will bring with me for DIY Expo in Goteborg.....U plate-cathode PCC88 = 130v, Ia = 5,4 ma, Cathode shunt "Panasonic" with very clear sounding. Interstage caps K40-Y9 or ФТ-3, I will listening some days and will decide. Output tranies -
big excellence Hammonds 125FSE. Output power is 1.5 Watts per channel /triod mode/, but sounding is like 2A3

Yesterday I decided to throw away interstage caps that I tried /ФТ-3, K40-Y9, Auricap, Mallory..../
and I put interstage transformer Hammond 124B, small, but very suitable for small currents /5-6 ma/ and for tubes with low Ra /PCC88, 6N1P, 6N23P, E80CC...../ Transformer's primary Ra = 10 kohm.
I used one section of secondary coil. The sound is a level high and better, very clear, detail, with strong bass. I was very surprised!!
I'd like advise You try it! /Don't forget connect 10-15 kohm, the same, like Ra, short to one section of secondary coil, or 20-25 kohm, if You use full secondary coil to doubling the signal for driving output tube, if it needs, and don't see it's parameter 150-15000 Hz, I heard very good last string of acoustic bass, and I measured linearity between 35-18000 Hz!/.
BTW....I didn't find EDCORS's interstage transformers in their prod. list...

[EWBrown]

That's good news about the 124Bs! I have four of them that I acquired several years ago, back when they were still inexpensive, but I never really got around to using them, as I figured they were of less than "optimum" quality. I was thinking of using them in a 1950s vintage 807PP AM plate modulator design, or a "weird" PP guitar amp, but with your discovery, I'll have to put them to a much better use.

If you want to keep DC off the primary winding, then a parallel RC or LC feed would accomplish that, and would probably improve the sound even more.

THere is also an interesting design line stage which uses the 124Bs and 6J6s, called the "Nickel Wonder", and I should have it posted elsewhere on this forum. Or find it here: http://wardsweb.org/LSB/11_06_04/6j6.jpg



Clixk on the little "+" in the upper left corner, for the full-sized image.

Triode Electronics also has some "universal" interstage traisnformers, UIS-1 which have a 20K CT primary and four separate 5K secondaries which can be arranged in many different ways., for 5K, 20K, or even 80K, CT or single ended.
These are significantly larger than the dimunitive Hammond 124Bs

/ed B

[azazello]

I tried different shunt resistors for half of secondary coil:
1. If use 15-20 kohm linearity of LF starts from 70-60 Hz.
2. If use 12-13 kohm _____________________ 50-60 Hz.
3. If use 10 kohm _____________________ 35-40 Hz.
Linearity of HF is more 18-20 kHz.
Now I use 10 kohm and sound is unbelievable bright and clear!
Now they cost in http://www.tubesandmore.com/ -Hammond interstage tr. 36 $, but I founded in the same price list, IMO, maybe the same /P-T 156/ for 17 $!

[EWBrown]

When I got my 124Bs 7 years ago, they were a lot lower cost than $36, but, as with everything else, the prices are always increasing over the years...

The nominal impedances for the 124B are 10K primary and 90K CT secondary, or a voltage / turns ratio of 1:3, and 1:1.5 for each side of CT,
this was a "Standard" for must small interstage trannies since the 1940s if not earlier. The nickel core striping definitely helps to extend the frequency response, as does properly loading the secondary as you have done.

I made inductance and DCR measurements last year, at 100Hz (my LCR meter's lowest test freq) the primary measured 101H and the secondary 800H. DC resistance of the primary is 415 ohms, the full secondary, 1570 ohms between the green leads. From the CT, 840 ohms and 730 ohms. (DC resistance imbalance is a result of the layered "solenoid" winding method).

With these relatively high inductances, I am presuming that the cores are NOT airgapped, but are interleaved. Power is rated at 5 milliwatts.

Date code is 3/24/04, so these trannies are approx seven years old.

With 10K across one half of the secondary, the primary would behave as if it was 4.44K (10K / 2.25). So, 40K across the entire winding would behave the same, and 20K across the full winding would reflect as 2.22K on the secondary.

For driving PP grids, the optimal loading would be somewhat different, as each grid would be receiving approximately half of the full waveform of the audio signal

I foresee some interesting experimentation in my near future

/ed B in NC

[katabatic]

Two more small amps, that I completed last month.





/ed B in NC

I've now completed my version of the 6bm8 amp (Ed's one on the right). I used a Hammond 369x power transformer, Edcor GSXE 10-8-5k output transformers, and Soviet-era 6f3p tubes. Coupling caps are Russian K40-Y-9's. It sounds great, a little 'darker' than the Get*Set*Go and Darling that I've built previously (darker meaning, I think, more pronounced bass). I used both NFB bits, the one in the original schematic and Ed's 1 meg resistor version. Many thanks to Ed and Ty for putting the plans up here.

George

[EWBrown]

Very nice! Much neater layout and wiring than my 6F3P / 6Ф3П / 6BM8 amp, which was wired in "layers" because of the limited under-chassis space.

If I were to do this again (and I probably will) I won't try to make it so small and crowded.

I would imagine the Edcor GXSE10-8-5K OPTs would sound even better than the smaller TF103s.

As previously mentioned, I found that the dual-NFB approach seemed to work the best. I've tried this with other tubes, with lesser results. Must be something unique to the 6BM8 family

Almost time for me to head to the neighborhood Memorial Day Weenie Roast

/ed B