Hi Peter,
your amp looks great ! Glad that you enjoy it so much as well
Where did you get the trafo covers ? They look very professional.
With regard to the heatsinks for your current sources, you may fix them to the PCB with hot melt glue (provided that they don't get extremely hot in use ...). That should at least protect the leads of the LM317s when transporting the amp.
Also, I would recommend securing the Mundorf caps with hot melt glue to the PCB. That not only helps for a safer long-time connection, but also can damp vibrations that originate from the power transformer ...
Best regards, Claas
your amp looks great ! Glad that you enjoy it so much as well
Where did you get the trafo covers ? They look very professional.
With regard to the heatsinks for your current sources, you may fix them to the PCB with hot melt glue (provided that they don't get extremely hot in use ...
). That should at least protect the leads of the LM317s when transporting the amp. Also, I would recommend securing the Mundorf caps with hot melt glue to the PCB. That not only helps for a safer long-time connection, but also can damp vibrations that originate from the power transformer ...
Best regards, Claas
Hi Claas,
Thanks! Good idea with glueing the capacitors. I'll check if if works for the heatsinks as well.
The transformer covers came from Aliexpress:
PAPRI 1PCS 85*85*100mm DIY Black Metal Transformer Cover Case Box HIFI Protect Cover Enclosure For Audio Tube Amplifier-in Amplifier from Consumer Electronics on AliExpress - 11.11_Double 11_Singles' Day
There are different sizes...
Thanks! Good idea with glueing the capacitors. I'll check if if works for the heatsinks as well.
The transformer covers came from Aliexpress:
PAPRI 1PCS 85*85*100mm DIY Black Metal Transformer Cover Case Box HIFI Protect Cover Enclosure For Audio Tube Amplifier-in Amplifier from Consumer Electronics on AliExpress - 11.11_Double 11_Singles' Day
There are different sizes...
I'm thinking of that coupling method (well, kinda any DC coupling method) between the first two stages, and what happens on the power-up when tubes are cold and don't conduct.
Basically we have almost half of the B+ on the second tube's grid (4.3k+30k+1M and 1M divider) and the cathode is still at the ground level.
Might that be a problem or am I overthinking?
Basically we have almost half of the B+ on the second tube's grid (4.3k+30k+1M and 1M divider) and the cathode is still at the ground level.
Might that be a problem or am I overthinking?
I had running mine with a tube rectifier for the B+ first, and now for several weeks with a silicon rectifier and regulated B+ that comes up way before the tubes heat up.
So far, no issues either way with my 6N1Ps that I could notice.
Might not be a significant issue after all.
Regards, Claas
So far, no issues either way with my 6N1Ps that I could notice.
Might not be a significant issue after all.
Regards, Claas
Replace EL84 with 6P1P
Hi Bas,
With the 6P1P versions, did you make any changes to the circuit to accommodate the lower gain of 6P1P? I assume that we can replace 6N1P with other tubes but not sure how that will change the performance of the amp.
Hi Bas,
With the 6P1P versions, did you make any changes to the circuit to accommodate the lower gain of 6P1P? I assume that we can replace 6N1P with other tubes but not sure how that will change the performance of the amp.
Tubecad vs Baby Huey in sound
Hi Bas,
I have a 12AX7/6P1P PP amplifier that I assembled based on a kit from China. It was currently set up as a 12AX7 SRPP driving differential triode output with no feedback. This amp sounds amazingly good with the limited power on my 93 dB speakers.
However, I was thinking to "upgrade" it. I saw you have built both Tubecad and Baby Huey amps based on EL84. I have EL84 tubes and is interested in building the original Tubecad or Baby Huey. Can you comment on the sound of them? Which one would you recommend me to build?
By the way, I have another triode strapped 6AR6 single ended amp. It sounds a bit warmer than the 6P1P PP. I have done some LTspice modeling. Both Tubecad and Baby Huey have low 2nd order harmonic. Both my 6AR6 and 6P1P have more 2nd order harmonic. I am interested to test one out to compare against my 6AR6.
Hi Bas,
I have a 12AX7/6P1P PP amplifier that I assembled based on a kit from China. It was currently set up as a 12AX7 SRPP driving differential triode output with no feedback. This amp sounds amazingly good with the limited power on my 93 dB speakers.
However, I was thinking to "upgrade" it. I saw you have built both Tubecad and Baby Huey amps based on EL84. I have EL84 tubes and is interested in building the original Tubecad or Baby Huey. Can you comment on the sound of them? Which one would you recommend me to build?
By the way, I have another triode strapped 6AR6 single ended amp. It sounds a bit warmer than the 6P1P PP. I have done some LTspice modeling. Both Tubecad and Baby Huey have low 2nd order harmonic. Both my 6AR6 and 6P1P have more 2nd order harmonic. I am interested to test one out to compare against my 6AR6.
While the Baby Huey sounded amazing on the first speakers I played them on. I've since been disappointed on other speakers. (I should try them on those speakers first again I guess) I think something is broken in that amp. (Still have to find out what...because the voltages and currents check out). I did build a tubecad but not with EL84's. But with 6p1p. I'm too afraid to recommend things anymore.
I couldn't' agree more with you, Bas. I also had built the Baby Huey a while ago and I must say that I never liked it. I have tried it with TQWT single driver speakers (with Fostex FE-167), single driver horns (with Fostex FE-206) and, mainly, with my current speakers, the Tune Audio Marvel 2-way horns. The sound always seemed to be constrained, flat, without speed and lacking in upper and lower frequencies.
Recently, I decided to try and change it to the Morgan Jones's Bevois Valley circuit, since the task was easy. My findings, so far (because I'm still trying various things), is that with NFB it sounds worse than the Baby Huey (in fact, my speakers never liked NFB - currently I'm listening to 2 different amplifiers: a pair of 300B monoblocks and a Cubie2 SS with lateral MOSFETs, both with 0NFB). So, I tried eliminating the NFB and the result was a revelation: a difference between night and day!
In a second attempt, I decided to try a different tube in the driver/splitter, namely the Russian 6N6P, since it has a slightly lower μ than the 6N23P-EV I originally tried and gain with this tube and 0NFB was a bit high. Using the same anode/cathode resistors as those with the E8CC circuit, I had the impression that it sounded better, but I'm now studying to find better working conditions for the 6N6P.
One second thought was to try triode connected EL84s (now I'm running them in UL mode), since my speakers are quite sensitive (96 dB) to be fed by a lower power amplifier. Hence, I found this thread in search for triode connected EL84s in PP.
And, since I'm in this thread, I have the following question, if someone could give me an answer: In UL mode, the EL84 is run at ca. 40 mA. According to the Mullard datasheet, when triode connected, it is suggested to run the tubes at just 24 mA. That's too low for a 12 W tube. Why not increase the current to, say, 35 mA?
Operating points are relative. It could be that the Mullard engineers were going for the highest possible output power from EL84-triode, therefore high plate voltage and lower plate current for Class-AB operation (instead of Class-A).
Operating points for an output tube coupled to an output transformer are even more relative. You could draw a loadline to try to get to the best compromise.
Triode-connected, into an 8k plate-to-plate OPT primary, I suppose you could run EL84s with 300V plate-to-cathode and 40mA plate current (each tube).
--
If you're going to run PP EL84s with no negative feedback, I'd say triode wired (to lower output impedance) would be a better bet than UL mode.
Operating points for an output tube coupled to an output transformer are even more relative. You could draw a loadline to try to get to the best compromise.
Triode-connected, into an 8k plate-to-plate OPT primary, I suppose you could run EL84s with 300V plate-to-cathode and 40mA plate current (each tube).
--
If you're going to run PP EL84s with no negative feedback, I'd say triode wired (to lower output impedance) would be a better bet than UL mode.
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Mercury99 and others,
Scenarios that I keep seeing in multiple Tubes / Valves threads like this:
I built this push pull amplifier (A). I like how it sounds. What can I do to improve it?
I prefer the sound of my single ended amplifiers, and another push pull amplifier (B) which has more 2nd harmonic distortion than push pull amplifier (A).
. . . Perhaps what you mean is, make it sound more like the amplifiers I prefer.
Building a third amplifier (C), on the hopes that is will sound more like amplifier (B), or like the single ended amplifier you like, can be a lot of trouble, especially if you do not like its (C's) sound any better than amplifier (A).
Why not try the following modifications first? . . .
Easy to do, lots less work than investing in lots of parts, and lots of effort to build amplifier (C).
1. Purposely Un-Balance the phase inverter stage of amplifier (A); or if present, the driver stage that follows the inverter (some stages function as both the inverter and driver stage . . . unbalance it).
Depending on the circuit, all you need to un-balance that stage is one single resistor, to lower the gain of one, and only one phase.
This will give more 2nd harmonic distortion, especially if there is little or no global negative feedback.
(do not un-balance the output stage).
2. If the damping factor of amplifier (A) is significantly greater, versus both amplifier (B) and the single ended amplifiers, then . . .
Reduce the damping factor of amplifier (A) by putting a single resistor in series with amplifier (A)'s output terminal and the speaker.
These may, or may not, cause amplifier (A) to sound more like the other (preferred sound) amplifiers.
3. More details of the amplifier that you want to improve, like its schematic, and more details of your loudspeaker's impedance versus frequency; or at least its DCR at its input terminals and its nominal impedance rating . . . will all be helpful to finding possible working suggestions to get the sound you want.
Scenarios that I keep seeing in multiple Tubes / Valves threads like this:
I built this push pull amplifier (A). I like how it sounds. What can I do to improve it?
I prefer the sound of my single ended amplifiers, and another push pull amplifier (B) which has more 2nd harmonic distortion than push pull amplifier (A).
. . . Perhaps what you mean is, make it sound more like the amplifiers I prefer.
Building a third amplifier (C), on the hopes that is will sound more like amplifier (B), or like the single ended amplifier you like, can be a lot of trouble, especially if you do not like its (C's) sound any better than amplifier (A).
Why not try the following modifications first? . . .
Easy to do, lots less work than investing in lots of parts, and lots of effort to build amplifier (C).
1. Purposely Un-Balance the phase inverter stage of amplifier (A); or if present, the driver stage that follows the inverter (some stages function as both the inverter and driver stage . . . unbalance it).
Depending on the circuit, all you need to un-balance that stage is one single resistor, to lower the gain of one, and only one phase.
This will give more 2nd harmonic distortion, especially if there is little or no global negative feedback.
(do not un-balance the output stage).
2. If the damping factor of amplifier (A) is significantly greater, versus both amplifier (B) and the single ended amplifiers, then . . .
Reduce the damping factor of amplifier (A) by putting a single resistor in series with amplifier (A)'s output terminal and the speaker.
These may, or may not, cause amplifier (A) to sound more like the other (preferred sound) amplifiers.
3. More details of the amplifier that you want to improve, like its schematic, and more details of your loudspeaker's impedance versus frequency; or at least its DCR at its input terminals and its nominal impedance rating . . . will all be helpful to finding possible working suggestions to get the sound you want.
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Hi kenev,
I have built the John Broskie / Tubecad EL84 PP amp. I run my EL84s triode-connected, on 8k Ohm output transformers, at 320V B+ (about 317V anode-cathode), and about 36 mA current through the EL84. (Actually, I am using 6P14P-EV)
Also, my experiments with 6N6P seem to confirm what an amp designer of a 6N6P headphone amp has told me once: this tube likes lots of current. He told me, up to 30 mA - I find that if you come into the region of 20 mA current, the 6N6P is really transparent sound-wise, with a lot of drive. If run at significantly lower currents, I always find its sound a bit muffled compared to, say, a E182CC or 5687.
Regards, Claas
I have built the John Broskie / Tubecad EL84 PP amp. I run my EL84s triode-connected, on 8k Ohm output transformers, at 320V B+ (about 317V anode-cathode), and about 36 mA current through the EL84. (Actually, I am using 6P14P-EV
)Also, my experiments with 6N6P seem to confirm what an amp designer of a 6N6P headphone amp has told me once: this tube likes lots of current. He told me, up to 30 mA - I find that if you come into the region of 20 mA current, the 6N6P is really transparent sound-wise, with a lot of drive. If run at significantly lower currents, I always find its sound a bit muffled compared to, say, a E182CC or 5687.
Regards, Claas