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Old 30th September 2005, 08:22 PM   #1
Cassiel is offline Cassiel  Libya
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Default Poindexter's 6v6 PP amp

Hi,


Im gonna build Poindexter amp for a friend. My question is:
The input tube is a 5965, here in europe difficult to find, any subtitutes? Amperex mentioned a 6922, any change in the schematic for using this tube?
Thanks.

Al.
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Old 30th September 2005, 09:17 PM   #2
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12AV7 and E180CC are similar. For 6922, filament pins are different - plus you'll have to bias it properly. Pretty much automatic if a constant current source is used.
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Old 30th September 2005, 10:11 PM   #3
amperex is offline amperex  United States
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I did not have to rebias for the 6922. The Siemens 6922 A0 code are great sounding tubes.
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Old 30th September 2005, 11:57 PM   #4
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if you use a CCS in the tail of the input stage you can get away with almost anything. The regulated current will set the plate voltage, and allow automatic biasing.

Amperex: where in MI? hopfully somewhere in the AnnArbor/Detriot metro?
cheers,
Doug-in-Dearborn
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Old 1st October 2005, 11:46 AM   #5
Cassiel is offline Cassiel  Libya
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Ok, good to hear i don't have to do a thing with the bias. I'll just leave it as it is and try to get that Siemens 6922.


Thanks all for the answers.

Al.
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Old 1st October 2005, 02:39 PM   #6
amperex is offline amperex  United States
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Yes, Siemens 6922 with the gold pins. I rolled a lot (I mean a huge lot) of different 6DJ8, 6922 & 7308s plus other types. The Siemens was the second best tube. It was ever so slightly 'edged out' by the very rare Raytheon 6CG7 black plate in the red/white/blue box. The Raytheon 6CG7 only provides about 14 volts output with one volt input. It requires a line-stage preamp for full volume.

Raytheon 6CG7 or any Raytheon with a 6CG7/6FQ7 in the white with red color box are made in Japan (stay far away from that tube). The Siemens were at its voltage limit as I used 330 volts on the B+ rail, but the tubes never arc'ed over. At the 'poinz' design of 315 volts B+, no problem. Do understand the 6922 barely provides full power output. At the common bias of -20 volts in the 'poinz' design, the 6922 provide up to 18 volts or so output. A high quality line-stage preamp does provide slightly better dynamics with the 'poinz' amp. You can go this route at a later date.

I also tried many 5965, Amperex pinch waist E180CC (and other E180CC), 12AV7, etc. Forget it, the Siemens 1960s era A0 code with grey shield as viewed at the top mica area were very nice tubes. Also, RCA imported Siemens to the USA during the early 1960s. The RCA boxes are usually stamped in black ink 'Made in germany' & same is on the tube glass. Per my 2 cents, you just can not go wrong with this 'poinz' design tube amp & the 6922.

The new manufacture Electro Harmonic 6V6 or believe it or not GE 6V6GTA 'coin base' tubes are very good.
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Old 1st October 2005, 02:54 PM   #7
amperex is offline amperex  United States
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Default Bandersnatch

I live in Lake City, MI next to Houghton Lake, MI.
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Old 1st October 2005, 03:32 PM   #8
amperex is offline amperex  United States
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Default I better add this......

Do not compromise the design with less than better quality parts as mentioned on the 'poinz' site.

My amps are monoblocks with Vishey resistors, AuriCap coupling caps, MQ iron, an LCLC power supply (each amp) using an oil cap on the output. Another LC section feeds the phase-splitter tube with a Solen polyproplyene cap. Electrolytic is not good in that position! The AuriCap requires 20 hours to sound good & over 100 hours to smooth out in the high frequency registers.

Do not use less than a 8k primary audio transformer with 300 to 315 volts plate. 10K would be better if one could be found. I use about 5.6K primary with parallel PP 6V6 tubes.

The rectifier that handily outperform the others I auditioned are the Sylvania 5R4GYB black plate. The tube is the design with the plates spaced 1/8" from each other in the center.

A few of us will state these amps ever so slightly outperformed a PP 45 I built with the same chassis, power supply design, quality nickel core MQ iron (both amps use MQ), a direct coupled 6P5GT to 6SN7, and same rectifier tube. The PP 45 amps outperformed a well known SET 45 on high-efficient quality speakers in the upper & lower audio frequencies per the new owner. A SET does have a pleasing midrange that is almost intoxicating to many audiophiles. The PP45s outperformed the standard amp with the 5965 tube. I did hear some somewhat pleasing midrange warmth with a RCA 5965 triple mica tube.

It may appear to some I am bragging. Not so, just what four audiophiles heard including myself. All of us prefer a neutral sounding amp without any midrange smearing often called warmth. Sonics are subjective & all audiophiles hear differently. The stock 'poinz' 6V6 amps are excellent & an inexpensive design superior to many amps. One design intent is to eliminate an expensive preamp that many simply can not afford & keep parts costs within reason.

If I insult some by sounding like a 'know it all', no flamer intended. I have much to learn in audio.
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Old 1st October 2005, 06:20 PM   #9
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Hey-Hey!!!,
I would suggest hunting for output Iron which offers some use past the amp it was first purchased for. Out of the latest amps I have designed and built, only one will stay together and remain while a second set of Iron is acquired.

Amperex, you are a bit out of my easy travelin' radius. Do try to visit if you're in the neighborhood. I'd love to have you and your gear over for a listen.

I found an easy way to get custom Iron: have it wound to spec. Heyboer is one of my favourite sources. They are the only source of audio Iron which will send the bill with the Iron, and expect the funds within 30 days. They even did this for the first stuff I ordered, fromthe first I telephoned them and worked out the details. Power Iron, signal Iron, and output Iron.

Heyboer is making the custom 10k output for me. 2 pairs of E-Linear taps, one for the front end, and the other at a different percentage for the g2/U-L connection. One spare pair for experimentation while I was at it, for 20%, 30%, and 40%. The basemodel OPTx I used for a model has a versatile winding geometry for applying taps at the end of the layers in 10% increments. AFIK, they are the only filks who are comfortable doing this. Suprisingly, I approached MQ about this and was refused on the tapping issue. Their loss, as that amp works very well, and it is sooo simple.

I do like pentodes for simple amps. Two stages, single B+, short path NFB and Class A bias on the finals. I have a HY69 amp like this, and am building a big brother to it, with the 5X125B. Good ole Thoriated Tungsten filaments. Fixed bias, cascode front end and my E-Linear NFB scheme.

It requires some CCS-es,but depletion-mode MOSFET ones are not soooo hard. Look on Bas Hornman's page for the DN2540N5 battery and non-battery circuits. Watch dissipation ratings on them, w/o heatsinks, stay below a Watt for the TO220 versions. The LND150N3 don't dissipate much heat and are fine with the TO92 case.

I put the name Merlin to this one, and am playing with it on the ART forum. Aprelim schematic is on the linked projects page:

http://audioroundtable.com/GroupBuild/Projects/

On parts, motor-run caps for the PS. Choke input filter, vacuum diode rectifiers. Oil film caps for the coupling, and PP grid chokes of 250/1k Hy inductance. Mills resistors for the two plate loads. L-C filter for the bias supply using Schottky diodes for minimum noise. Good quality 'lytics for its filters.

When you stay simple, there aren't too many parts to inflate the bill. There is of course more to the Merlin amp, but the simple approach is *VERY* nice.
cheers,
Douglas
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Old 1st October 2005, 06:44 PM   #10
amperex is offline amperex  United States
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If I plan a trip your way, we will compare systems. It could be quite educational to both of us. Your amp design looks good. I bet it is a great performer.

I have made great progress in modifying my Pro Ac 2.5s to superior performance.

I have a third generation DIY preamp & starting a forth design.

I finished my latest tube type FM tuner & I am calling it good. It rivals some CDs on the best FM station, but most would never believe that 'CD' statement of mine.
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