Hi!
Maybe some of you (or know someone) built a push-pull amp using those tubes. I could get Hammond 1650FA output transformers or make an order at Electra-Print...However there could be a "vintage alternative"! Some people put 6P14P-ev in their vintage amp instead of 7189 (saw someone did it in a PACO SA-40).
Suggestions?
Thanks
Pierre
Maybe some of you (or know someone) built a push-pull amp using those tubes. I could get Hammond 1650FA output transformers or make an order at Electra-Print...However there could be a "vintage alternative"! Some people put 6P14P-ev in their vintage amp instead of 7189 (saw someone did it in a PACO SA-40).
Suggestions?
Thanks
Pierre
If you're building it from scratch you can use 6P1P with minimal changes (bias point and pinout) and they cost much less than 6P14P/EL84. They are electrically a 6V6 with a slightly lower power/voltage rating. Since you're in Canada if you're interested shoot me a PM. I have a quantity of them.
Pierre:
You need a 8 K transformer for your tubes. For vintage alternative, you may consider transformers from amplifiers that used 7189, 6BQ5, or 6V6 tubes. Scott 299c used huge output transformers of reasonable quality. These transformers are conservatively rated 18 W and can go subsonic (my personal experience). Stancor A-8072 is even bigger and is rated 25 W; it has UL taps. This is what I had positive experience with.
Fisher, Eico, Harman-Kardon, Pioneer, Sansui, etc. etc. made good quality amplifiers with these tubes. All major transformer manufacturers (Stancor, Thordarson, Merit, UTC, Triad, etc. had 8 K HiFi transformers in their catalogs - you need to find catalog numbers. All these transformers regularly appear on eBay and go for about $100-150 apiece. It may seem expensive, but custom-wound transformer will cost more.
Also, you should be aware that 6P14P (and 6BQ5) have different biasing than 7189. I had to change biasing in my Scott 299c when substituting 7189 for 6P14P.
You need a 8 K transformer for your tubes. For vintage alternative, you may consider transformers from amplifiers that used 7189, 6BQ5, or 6V6 tubes. Scott 299c used huge output transformers of reasonable quality. These transformers are conservatively rated 18 W and can go subsonic (my personal experience). Stancor A-8072 is even bigger and is rated 25 W; it has UL taps. This is what I had positive experience with.
Fisher, Eico, Harman-Kardon, Pioneer, Sansui, etc. etc. made good quality amplifiers with these tubes. All major transformer manufacturers (Stancor, Thordarson, Merit, UTC, Triad, etc. had 8 K HiFi transformers in their catalogs - you need to find catalog numbers. All these transformers regularly appear on eBay and go for about $100-150 apiece. It may seem expensive, but custom-wound transformer will cost more.
Also, you should be aware that 6P14P (and 6BQ5) have different biasing than 7189. I had to change biasing in my Scott 299c when substituting 7189 for 6P14P.
Thanks but I already bought some 6P14P-ev tubes. Also, I'll probably build something like "El Cheapo".
Yes some guys give a description of their "restauration experience". This is often very interesting. Thanks for exemples!
The Russian 6П14П-EB (6p14p-ev), AKA EL84M, is a true, very rugged, 7189 equivalent. We are lucky to have the variant. Otherwise, many a fine "vintage" piece of equipment would be parted out. 
Sherwood squeezed 20 WPC out of 7189s in their S5000 integrated amp. Whenever a GNFB loop is employed, magnetic headroom in the O/P "iron" is essential. Lack of magnetic headroom leads to core saturation and wretched sound.
For 20 W., use "iron" rated for 35 or 40 W. Unfortunately, none of Hammond's offerings is really suitable. Rated at 50 W., Edcor's CXPP50-8K is "overkill", but definitely will work and may, in fact, be the least expensive option.
Sherwood squeezed 20 WPC out of 7189s in their S5000 integrated amp. Whenever a GNFB loop is employed, magnetic headroom in the O/P "iron" is essential. Lack of magnetic headroom leads to core saturation and wretched sound.
For 20 W., use "iron" rated for 35 or 40 W. Unfortunately, none of Hammond's offerings is really suitable. Rated at 50 W., Edcor's CXPP50-8K is "overkill", but definitely will work and may, in fact, be the least expensive option.Attachments
I use this circuit. More complexity but less expensive to build. Ignore the 340V as I designed it to push worn out tubes
"The constant-current source is only being shunted by a 10k resistor, which can be safely ignored. On the other hand, if the crescendo takes an output tube outside the class-A envelope, the rightmost diode will begin conducting and effectively couple the capacitor to the cathodes, which will greatly limit their AC movement away from the established DC bias voltage. Of course, if the increased volume is sustained for long enough, the capacitor will charge up to a much higher voltage. But once the volume falls to normal, the leftmost diode will begin conducting, allowing the capacitor to discharge through the constant-current source."
"The two large capacitors effectively couple the two cathodes in AC terms, but allow each tube to find its own DC bias voltage. The 1M resistor establishes a polarizing voltage across each capacitor." John Broskie.
"The constant-current source is only being shunted by a 10k resistor, which can be safely ignored. On the other hand, if the crescendo takes an output tube outside the class-A envelope, the rightmost diode will begin conducting and effectively couple the capacitor to the cathodes, which will greatly limit their AC movement away from the established DC bias voltage. Of course, if the increased volume is sustained for long enough, the capacitor will charge up to a much higher voltage. But once the volume falls to normal, the leftmost diode will begin conducting, allowing the capacitor to discharge through the constant-current source."
"The two large capacitors effectively couple the two cathodes in AC terms, but allow each tube to find its own DC bias voltage. The 1M resistor establishes a polarizing voltage across each capacitor." John Broskie.
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That is what the op wrote.
This and the presented schematic with auto bias and 340 V +Ub works fine with
Hammond 1650FA. No more than 15 W can be expected.
Have you tested that this really is the case ?
I have noticed that the specifications do not allways tell the truth. As an example, below is the link to 40 VA OPT, but I have tested it to work fine up to 100 W.
TGL 40/001 INDEL - Transformer: speaker | TME - Electronic components
This and the presented schematic with auto bias and 340 V +Ub works fine with
Hammond 1650FA. No more than 15 W can be expected.
Have you tested that this really is the case ?
I have noticed that the specifications do not allways tell the truth. As an example, below is the link to 40 VA OPT, but I have tested it to work fine up to 100 W.
TGL 40/001 INDEL - Transformer: speaker | TME - Electronic components
Check Hammond's specification sheet out. 30 Hz. is the claimed low freq. for full power handling. Magnetic headroom is lacking exactly where it's most needed.
Ah this is the catch! I had in mind to use the tubes in pentode mode (with G2 voltage regulated). A nice pair of vintage OPT maybe? Anyway I'm not in a hurry. Slowly collecting parts.
Check Hammond's specification sheet out. 30 Hz. is the claimed low freq. for full power handling. Magnetic headroom is lacking exactly where it's most needed.
At the proximity of bass resonance the impedance of a typical loudspeaker is high.
Therefore the power level at this frequency region is much less than at higher frequencies.
An externally hosted image should be here but it was not working when we last tested it.
Nice speakers, no question about it. But if they are fed 30 Hz at 20 W level, 80-90% of the output will be harmonic distortion. Real 30 Hz at 20 W and 90 dB efficiency in home listening environment will shake walls, rattle furniture, and break windows.
It is notoriously difficult, I would say impossible to reproduce deep bass through small speakers at reasonable fidelity. Small speaker relies on long cone excursion for bass, which is a recipe for distortion.
Amen. I can only add that low organ pedal tones require something like Notre Dame cathedral to sound right. Organ doesn't sound right in concert halls. I was much disappointed by organ low tones in LA Phil Disney Hall, which is praised for being an almost acoustically perfect concert venue. When organist takes low notes, the sound goes d-r-r-r-r. Sounds below 40 Hz you hear not with your ears, but with your whole body.
To moderators - this is not hijacking the thread. This is raising a relevant question - do you really need full power 20 Hz capability in a 6BQ5 output transformer?
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