Since el84 need little in the way of signal swing, and modern sources can provide healthy signals on their own, the pentode input of the kel is probably unnecessary.
The 2nd looks to be a simplified variation on El Cheapo.
There are 3 EL84 PP that have been developed on the forum. Baby Huey, El Cheapo, and The Red Light District. I would recommend one of those.
We built a variation on El Cheapo (triode Class A) and it is stellar. I have the biasing LED construct for the Red Light District, but would build baby Huey next.
You have to work really hard to make a bad EL84 amplifier.
dave
There are 3 EL84 PP that have been developed on the forum. Baby Huey, El Cheapo, and The Red Light District. I would recommend one of those.
We built a variation on El Cheapo (triode Class A) and it is stellar. I have the biasing LED construct for the Red Light District, but would build baby Huey next.
You have to work really hard to make a bad EL84 amplifier.
dave
Have a look at John Broskie's EL84PP (triode-strapped) circuit on his TubeCad Journal site as well:
PS-4 & PS-5 Tube Power Supplies
(scroll down to "EL84/6BQ5 Push-Pull Power Amplifier")
If about 6W is enough, it can be a very good-sounding circuit.
There a several threads on this design here, for example, look at:
Unexpectedly good EL84 amp
I have built this amp as well, and it is one of the best amps I have ever built 😀
(documentation in that thread from post #153 on - don't let yourself be disctracted by my bias ideas - John Broskie's original has a very simple auto bias design)
Best regards,
Claas
PS-4 & PS-5 Tube Power Supplies
(scroll down to "EL84/6BQ5 Push-Pull Power Amplifier")
If about 6W is enough, it can be a very good-sounding circuit.
There a several threads on this design here, for example, look at:
Unexpectedly good EL84 amp
I have built this amp as well, and it is one of the best amps I have ever built 😀
(documentation in that thread from post #153 on - don't let yourself be disctracted by my bias ideas - John Broskie's original has a very simple auto bias design)
Best regards,
Claas
Too bad the UL taps are at 40%, else you could have enjoyed losing the hair off your head by trying the Acrosound 20 DC coupled design.
Thanks for your answers!. The one with ECC82 will work fine? There are UL connection on my Hammond 1650E output tranformers, so I think i will go for one with UL connection.
Another choice
Like another poster said, the first circuit might have too much gain. The second circuit might not have enough, depending on your source. The second is a quasi Quad II-like design. The Quad used pentodes, the ECC82 is a low Mu triode.
I've built a couple of the Tubelab.com SPP and they work really well with Hammonds. This link has the circuit, scroll to the end. http://3wqmcw1jc4oh3afanm29507a-wpe...ds/2020/02/Part-3-Attachment-2-Revision-1.pdf
Review of SPP here: EL84 DIY Amp Project, Part 6 (Conclusion): Sonic Evaluation and Output Mode Options | Wall of Sound | Audio and Music Reviews
With your power transformer the B+ might be a bit low with a tube rectifier so you might want to go SS.
If you want to make tube bias adjustable without going to fixed bias see the attached circuit used in the DIY Tube Dynaclone.
Steve
Like another poster said, the first circuit might have too much gain. The second circuit might not have enough, depending on your source. The second is a quasi Quad II-like design. The Quad used pentodes, the ECC82 is a low Mu triode.
I've built a couple of the Tubelab.com SPP and they work really well with Hammonds. This link has the circuit, scroll to the end. http://3wqmcw1jc4oh3afanm29507a-wpe...ds/2020/02/Part-3-Attachment-2-Revision-1.pdf
Review of SPP here: EL84 DIY Amp Project, Part 6 (Conclusion): Sonic Evaluation and Output Mode Options | Wall of Sound | Audio and Music Reviews
With your power transformer the B+ might be a bit low with a tube rectifier so you might want to go SS.
If you want to make tube bias adjustable without going to fixed bias see the attached circuit used in the DIY Tube Dynaclone.
Steve
Attachments
ECC82 is not a very linear tube in voltage amplifier duty. Build the Baby Huey with similar topology based on 12ax7, plus drivers for the power tubes. Look for Baby Huey threads on diyAudio, there are several, but start with “EL84 amplifier - Baby Huey” by gingertube. There is even a Wiki here.
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Don't forget, with the Hammond 370HX, you must use a tube rectifier.
With Si-diodes the voltage is much to high for a EL84.Unless with a big series resistor to lose the exess (20W). But at the start the voltages will be still high, need for the electrolytics 450V or a delay on the HT.
Mona
With Si-diodes the voltage is much to high for a EL84.Unless with a big series resistor to lose the exess (20W). But at the start the voltages will be still high, need for the electrolytics 450V or a delay on the HT.
Mona
It is great to be a member of this forum. Remember in the seventies when i started to build amplifiers (ss). Found schematics from magazines, but we had no one ask if we got into trouble. Thanks again folks!
But Eli points out that with EL84 it is a good choice as its nonlinearities are opposite the EL84s, so you end up with a pretty linear combo.
dave
Well I don't like either one.
The Hammond has 0-4-8 and 16 ohm out.That is 4 ohm is the middle of 0-16, nice to make a cathode feedback output stage.
After some calculations and looking at the curves, this is what I cooked up.
The 5T4 is second choise, GZ34 is better but very expensive.
The connections to the 0 and 16 is a 50% chance, Hammond doesn't give the phase of the windings, could be the two have to be crossed.
Mona
Attachments
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Top left in the schematic is 200v, must be 170v (was leftover from trying with another tube)
Mona
Mona
Thanks 😎
I tryed diff tubes ECC81 ECC84 ECC85, the 200v was from the 84.
Thr 81 and 85 can both be used here.
Mona
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I see that the power transformer gives 275v x 2 on this curcuit. My Hammond 370HX have the same output. If I use an 5T4 i can use my Hammond transformer and get about 300v out?
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Hammond: 275V for 200mA DC
Without load the voltage from the transfo will be higher, say 290V (+5%)
Rectified you get 290x1,4=400V. With a load the voltage drops, lower transfo and loss in the tube.
Two amps are good for ~150mA DC.If there is still 280V on the transfo (not full load yet) the DC would be 390V if no loss from the tube.
How much one loose depends on the quality of the tube.Educated gess, 315V left.
Mona
The last EL84 amp I built used a Hammond 272JX, 300-0-300 volts. The newer 200 series Hammonds have pri taps for 115 and 125 volts IIRC. With my ~120VAC line and using the 125v pri tap, the filament voltages were 5.9 volts and 6.2 volts. The rectifier was a Sovtek 5AR4/GZ34. The total HT draw was about 190mA, the EL84s were running a bit "hot" at about 40mA each.
First cap after the GZ34 was 47uF, then a Hammond 1.5H 200mA choke, then a 150uF cap that supplied the OPT center taps. The EL84s wound up with about 307 VDC on their plates. Maybe a little high but OK on Russian EL84s.
So, with your power trannie (275-0-275) there might be a bit too much drop across a 5T4. The GZ34 has a fairly low drop, as rect tubes go, and might be a possibility if your B+ is a bit lower than desired.
Good Luck. Get those tubes glowing!
Cheers, Steve
First cap after the GZ34 was 47uF, then a Hammond 1.5H 200mA choke, then a 150uF cap that supplied the OPT center taps. The EL84s wound up with about 307 VDC on their plates. Maybe a little high but OK on Russian EL84s.
So, with your power trannie (275-0-275) there might be a bit too much drop across a 5T4. The GZ34 has a fairly low drop, as rect tubes go, and might be a possibility if your B+ is a bit lower than desired.
Good Luck. Get those tubes glowing!
Cheers, Steve