Just to be sure Ian, you have around -100V for the PI, two leds and R16 at 47 kOhm? So on a BH EL84 we should have around -35V and R16 at 15 kOhm.
Thanks in advance.
OK finally got back into my workshop with the BH. Here is the final tweaks report card.
Measurements before tweaks
B+ = 470V
B- = 105V
Bias on the KT77s is around -42 / -43 Volts for 40mA idle.
The V+ for the mosfet drain is +15.2
I had thought about fitting some 6550 in place of the KT77 but That B- is a bit low for either 6550 or KT88 so sticking with the KT77.
Did the 2nd red LED in place of R17 mod with R16 = 47K for approx 2mA LED current (For my B- of -105V).
This did improve the top end and remove that slight "muffledness" I noted earlier - RECOMMENDED.
I was using AC heaters and using the same single heater winding to feed the voltage doubler on the power supply board to derive that +15.2 volts for the mosfet drains.
I said earlier "no hum" - WRONG - there was some buzz at low level, but objectionable.
Fitted an extra 3VA power tranny to feed the voltage doubler so it was no longer fed from the heater supply, what I had on the shelf was a 9V secondary job so ended up with +22V for the mosfet drain supply, that is actually good.
Fitted 100 Ohm Psudo centre tap resistors to the heater supply and connected pseudo cntre tap to the +22V supply. That got rid of all my low level buzz/hum problems.
While I had it on the bench I soldered a 3M6 resistor across the 2M2 R8 on the power supply board (1M36 effective) to reduce the 555 delay on time to 57 seconds. I thought it was too long with just the 2M2. A 1M2 or 1M5 would be good for Power Supply Board R8.
Only job left now is to screw on the bottom cover. Happy with it.
Cheers,
Ian
Measurements before tweaks
B+ = 470V
B- = 105V
Bias on the KT77s is around -42 / -43 Volts for 40mA idle.
The V+ for the mosfet drain is +15.2
I had thought about fitting some 6550 in place of the KT77 but That B- is a bit low for either 6550 or KT88 so sticking with the KT77.
Did the 2nd red LED in place of R17 mod with R16 = 47K for approx 2mA LED current (For my B- of -105V).
This did improve the top end and remove that slight "muffledness" I noted earlier - RECOMMENDED.
I was using AC heaters and using the same single heater winding to feed the voltage doubler on the power supply board to derive that +15.2 volts for the mosfet drains.
I said earlier "no hum" - WRONG - there was some buzz at low level, but objectionable.
Fitted an extra 3VA power tranny to feed the voltage doubler so it was no longer fed from the heater supply, what I had on the shelf was a 9V secondary job so ended up with +22V for the mosfet drain supply, that is actually good.
Fitted 100 Ohm Psudo centre tap resistors to the heater supply and connected pseudo cntre tap to the +22V supply. That got rid of all my low level buzz/hum problems.
While I had it on the bench I soldered a 3M6 resistor across the 2M2 R8 on the power supply board (1M36 effective) to reduce the 555 delay on time to 57 seconds. I thought it was too long with just the 2M2. A 1M2 or 1M5 would be good for Power Supply Board R8.
Only job left now is to screw on the bottom cover. Happy with it.
Cheers,
Ian
Thanks Ian,
I've done a chart to calculate R17 value in your "R16 red led" mod:
I've done a chart to calculate R17 value in your "R16 red led" mod:
Code:
B- [V] R16 R17 [kOhm]
15 red led 5,8
20 red led 8,3
25 red led 10,8
30 red led 13,3
35 red led 15,8
40 red led 18,3
45 red led 20,8
50 red led 23,3
55 red led 25,8
60 red led 28,3
65 red led 30,8
70 red led 33,3
75 red led 35,8
80 red led 38,3
85 red led 40,8
90 red led 43,3
95 red led 45,8
100 red led 48,3
105 red led 50,8
110 red led 53,3
115 red led 55,8
120 red led 58,3
125 red led 60,8
130 red led 63,3
135 red led 65,8
140 red led 68,3
145 red led 70,8
150 red led 73,3Damn, Yes! Can the mods modify it?
the post #884 here and this other post: EL84 Amp - Baby Huey
the post #884 here and this other post: EL84 Amp - Baby Huey
Hello gingertube(Ian) and bandol83,
I have recently been gifted an old home amp that has some vintage Hammond iron. I have 2 of the Hammond 1626 Xfrmrs. I am inquiring if the data below makes them suitable for a 6V6 application like Ian has built. I am copying data from the 1974 Hammond catalouge.
AUDIO OUTPUT I TRANSFORMERS HAMMOND I 1600 SERIES - 10 Watt to 75 Watt Designed for Hi-Fi, Stereo or P.A. system applications (Tube circuits)..
Screen taps on 1626 (41 % of pri. turns); for ultra-linear operation if required.
Type 1626 - Frequency response 30 to 30 kHz (-1 dB ref 1 000 Hz minimum)
1626X, 20W, 6600 ct ohm P Imp., 80ma DC per side.
PS: I have 2 of the original BHEL34 pcb and most parts which will be used to build an higher power model.
I will be looking to purchase another set from prasi for the 6V6 if applicable or breakout my pcb design package and learn something. Either way are the above OPT good for the 6V6 or am I barking up the wrong tree.
Thanks for the help.
Myles
I have recently been gifted an old home amp that has some vintage Hammond iron. I have 2 of the Hammond 1626 Xfrmrs. I am inquiring if the data below makes them suitable for a 6V6 application like Ian has built. I am copying data from the 1974 Hammond catalouge.
AUDIO OUTPUT I TRANSFORMERS HAMMOND I 1600 SERIES - 10 Watt to 75 Watt Designed for Hi-Fi, Stereo or P.A. system applications (Tube circuits)..
Screen taps on 1626 (41 % of pri. turns); for ultra-linear operation if required.
Type 1626 - Frequency response 30 to 30 kHz (-1 dB ref 1 000 Hz minimum)
1626X, 20W, 6600 ct ohm P Imp., 80ma DC per side.
PS: I have 2 of the original BHEL34 pcb and most parts which will be used to build an higher power model.
I will be looking to purchase another set from prasi for the 6V6 if applicable or breakout my pcb design package and learn something. Either way are the above OPT good for the 6V6 or am I barking up the wrong tree.
Thanks for the help.
Myles
Ian previously wrote that he preferred a 10k primary in stead of 8k for his 6V6/6SL7 BH. You can read about it here and the following four posts:
https://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-226.html#post5718761
If I had 20W 6.6K output transformers I would plan to build a BH with 6L6G, or russian 6P3S (not the higher power -E version).
https://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-226.html#post5718761
If I had 20W 6.6K output transformers I would plan to build a BH with 6L6G, or russian 6P3S (not the higher power -E version).
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Thanks Francois,
I have read the threads and read about the flexibility of what can be used to build variations of the BH. Thanks for the info about the 6L6 family. I am looking at data sheets, to see if I can get a handle on THD values. I think I have found that max plate dissipation for the tubes is about 19 watts, so should be safe with my 20 watt OPT's?. Some data sheets are telling me that THD will be about 15% in Class A while others are telling me that THD will be about 2% in Class A. I will have to sort that, before moving on.
Let me know if you have any data that might help. Triode 6L6 is low watts out and Pentode is higher around 10-12 watts out. Again need some help to decide. Open to ideas.
MM
I have read the threads and read about the flexibility of what can be used to build variations of the BH. Thanks for the info about the 6L6 family. I am looking at data sheets, to see if I can get a handle on THD values. I think I have found that max plate dissipation for the tubes is about 19 watts, so should be safe with my 20 watt OPT's?. Some data sheets are telling me that THD will be about 15% in Class A while others are telling me that THD will be about 2% in Class A. I will have to sort that, before moving on.
Let me know if you have any data that might help. Triode 6L6 is low watts out and Pentode is higher around 10-12 watts out. Again need some help to decide. Open to ideas.
MM
Thanks Zintolo,
Read through most of your threads, but could not find any reference to the OPT's that you used for your el34 build. I am assuming they are above 20W.
I get the feeling that since my Hammond 1626 OPT's are only 20W & 6.6k, I am severely restricted as to what I can build. I am only looking for 10W - 20W of output power. I am really looking for some good suggestions from builders that know a lot more about this than I do.
MM
Read through most of your threads, but could not find any reference to the OPT's that you used for your el34 build. I am assuming they are above 20W.
I get the feeling that since my Hammond 1626 OPT's are only 20W & 6.6k, I am severely restricted as to what I can build. I am only looking for 10W - 20W of output power. I am really looking for some good suggestions from builders that know a lot more about this than I do.
MM
6v6gt or 6p6s an option as well, with a pentode/ul (Yves/Ian) switch, but I've always read that generally speaking the 6L6 family likes high loads to play better (10 kOhm and above).
Another option (to be checked) could be to connect a 8 Ohm speaker to the 4 Ohm tap and use it as 13.2 kOhm Raa with 6L6GC at 400 V to run in class A full time using the UL tap. You should have approximately 20 W in this configuration.
You can also mount an adaptor noval into octal and install an EL84 or equivalents. Mullard datasheet suggests 6.6 kOhm Raa for UL.
Another option (to be checked) could be to connect a 8 Ohm speaker to the 4 Ohm tap and use it as 13.2 kOhm Raa with 6L6GC at 400 V to run in class A full time using the UL tap. You should have approximately 20 W in this configuration.
You can also mount an adaptor noval into octal and install an EL84 or equivalents. Mullard datasheet suggests 6.6 kOhm Raa for UL.
Thanks for the info guys. So if I use the 6l6/7591 line, when I look up the tube data am I looking for pp triode or pp pentode data and am I looking for Class A operation or for Class AB1 operation. Very new to tubes and a lot of info to wrap ones head around.
One question also, do you plan for running tubes full tilt?. Say for example you have 2 tubes contributing 30W into a 20W Xfrmr, can the tubes run at 66% (lower voltage I assume) so as to not exceed the 20W and still sound good, or do you need to build for the higher power (hence better opt required).
Francois: I don't even know you, I only know of you through this thread. I know that you have been chastised before due to your rudeness on this forum. Please refrain from using " How many times do you have to be told", when replying to me. I am not a child and surely not one of your children.
MM
One question also, do you plan for running tubes full tilt?. Say for example you have 2 tubes contributing 30W into a 20W Xfrmr, can the tubes run at 66% (lower voltage I assume) so as to not exceed the 20W and still sound good, or do you need to build for the higher power (hence better opt required).
Francois: I don't even know you, I only know of you through this thread. I know that you have been chastised before due to your rudeness on this forum. Please refrain from using " How many times do you have to be told", when replying to me. I am not a child and surely not one of your children.
MM
The max plate dissipation shown in the data sheet is NOT the power going into the OPT. As the name implies, it is the maximum power the tube is able to dissipate as heat. The power seen by the OPT depends on the operating conditions.
Dear Kokanee,
I would suggest you to do what I'm trying to do: read old books and learn little by little something more about tubes and how to improve their working conditions.
If you have a specific question, open a thread and wait for replies. If they don't come, try to find the answer yourself and ask if it's correct. Do not pretend an answer.
I have to say that, based on the netiquette, write in a thread asking off topic questions of personal interest IS considered rude. Do it three times in a raw makes it even ruder. It is not a matter of being some of someone or not.
That said, enjoy the DIY.
I would suggest you to do what I'm trying to do: read old books and learn little by little something more about tubes and how to improve their working conditions.
If you have a specific question, open a thread and wait for replies. If they don't come, try to find the answer yourself and ask if it's correct. Do not pretend an answer.
I have to say that, based on the netiquette, write in a thread asking off topic questions of personal interest IS considered rude. Do it three times in a raw makes it even ruder. It is not a matter of being some of someone or not.
That said, enjoy the DIY.
Hi Myles,
With your OPT (1620) i would recommend a nice 6V6 push-pull.
See chart below from Hammond website.
BR
Eric
