With new diodes... all the same! Humdidum everywhere!!!!
Yes! Same symptoms here!
Yes, I know toroidy in poland! Great, clean stuff... very friendly people there...
This could be good too:
Frag Jan zuerst- Ask Jan first: Roehren und mehr
Their TRA200 under Katalog-Tranformatoren-Universalnetztrafos... has the wanted specs also! Ring or EL Kern???
What shall I do with Edcor now! I cannot prove that they might be making transfermators not determend for outside of North America... ? Or what?
😡😕
Well, maybe they need every penny nowadays... 🙂
Does somebody have a conclusion? Probably when I order a new trans from around the corner AND the amp is then dead quiet... 🙂
Yes! Same symptoms here!
Yes, I know toroidy in poland! Great, clean stuff... very friendly people there...
This could be good too:
Frag Jan zuerst- Ask Jan first: Roehren und mehr
Their TRA200 under Katalog-Tranformatoren-Universalnetztrafos... has the wanted specs also! Ring or EL Kern???
What shall I do with Edcor now! I cannot prove that they might be making transfermators not determend for outside of North America... ? Or what?
😡😕Well, maybe they need every penny nowadays... 🙂
Does somebody have a conclusion? Probably when I order a new trans from around the corner AND the amp is then dead quiet... 🙂
Hard to come to a conclusison without actually hearing what you hear...I would try one more thing before investing in a new PT:heat the tubes, but remove the hv, the two red connections of the Transformers - quiet?
Massiv hum....try to supply the hv from an external dc supply...should be quite then.Check the first filter capacitor, and you can as well add another 450v/100uf cap right behind the rectifier bridge and see if this changes anything
Just for fun I put 100uF/400V in front of 330/10W... but made even more hum...
How much HV should the DC supply have?
I have 12VDC power supply... or a battery 12V...
Or 24VDC I found...
So, please tell me how to hook up DC to the HV terminals? 🙂
I guess it won't work with 24V...
I will buy a new power trans... Is this one okay?
TRA200 from Jan Wuestens in germany... ca. 30€
Small mains transformer for tube applications such as small amps, preamps or as a replacement for tube radios.
Primary: 230 V AC, sec 1 : 230 V, 0,12 A ; sec 2: 20 V 0,12 A ; sec 3: 6,3 V 4 A for use with semiconductor bridge rectifiers.
66mm*82mm*58mm.
Made in Germany.
The 230V and the 20V secondaries can be series connected if desired.
Or TRA801 Ringkern from Jan Wuestens
prim : 2*115V
Sec1: 230V 130mA
Sec2: 20V 130mA
Sec3: 6,3 V 4 A , total.: 58VA
Size: D*H: 85*35mm²
Sec2 can be connected in series with Sec1
How much HV should the DC supply have?
I have 12VDC power supply... or a battery 12V...
Or 24VDC I found...
So, please tell me how to hook up DC to the HV terminals? 🙂
I guess it won't work with 24V...
I will buy a new power trans... Is this one okay?
TRA200 from Jan Wuestens in germany... ca. 30€
Small mains transformer for tube applications such as small amps, preamps or as a replacement for tube radios.
Primary: 230 V AC, sec 1 : 230 V, 0,12 A ; sec 2: 20 V 0,12 A ; sec 3: 6,3 V 4 A for use with semiconductor bridge rectifiers.
66mm*82mm*58mm.
Made in Germany.
The 230V and the 20V secondaries can be series connected if desired.
Or TRA801 Ringkern from Jan Wuestens
prim : 2*115V
Sec1: 230V 130mA
Sec2: 20V 130mA
Sec3: 6,3 V 4 A , total.: 58VA
Size: D*H: 85*35mm²
Sec2 can be connected in series with Sec1
Give it a try. If it is not the one causing the problem, you at leasr have a transformer in spare
Once you told me to check the first cap... now I did, it seems to be okay, measures 100.8uF... looks okay too! I replaced it though... still hums...
End of next week I will be back with good or bad news... 🙂
Transformer in spare...hahaha.. this will be my last tube amp diy challenge!
Thanks for your time!
End of next week I will be back with good or bad news... 🙂
Transformer in spare...hahaha.. this will be my last tube amp diy challenge!
Thanks for your time!
Mechanical hum from a power xformer is easy to diagnose: put a screwdriver against your ear with the handle end, and the blade on the xformer. If it is mech hum, it will be unmistakable coming through the screw driver.
As kids we used to chase engine noise that way. ;-)
For this once, you can trust your ears.
Jan
OK, hadn't picked that up. If you are sure about that. Did you try disconnect the speaker?
It wasnt meant as a cure for the hum 🙂) but to clearly identify the hum coming from the transformer....
The topic is lacking direct link to schematics, indeed: http://www.pmillett.com/file_downloads/midget_sch.pdf or
: : correction R7 K36-K39 is actually for PP with individual cathode bias networks; for this case of SE the K30-K33 is more appropriate
An externally hosted image should be here but it was not working when we last tested it.
wanna add my $0.05 of suggestions for afterwards fixing hum: - There was v.2 of MM schematics with 100V Zener replaced with 30K + 30K divider + el-cap. AFAIR the author mentioned that the divider sounded better, and that’s my own impression too; - I’d recommend to add 1 more LED to make it 3 between cathode and the suppressor grid (thanks to smoking-amp for suggestion based on bottom diagram page 6, for better plate characteristics squareness); - The output stage’s pentode mode works better with replacing R1 (K15) with a 12V Zener (1N4742) or you might use one up to 100V, whatever sounds best to your ear; - The thermal condition might be improved together with slightly higher output by replacing R7 with K36-K39 (1Wa is more than sufficient) and shunting it with a same 12V Zener. The 470 uF is perfect for this spot; - With these mods the 10K:8E trafo can be used with slight improvement on THD while the sound remains airy and pleasant. BTW, you could simply buy an APPJ Mini 1501 based on 6AD10 for the same money you spent on parts )) I extensively listened 6T10 vs. 6AD10 and could not hear any difference. Any others’ opinions on that comparison?
: : correction R7 K36-K39 is actually for PP with individual cathode bias networks; for this case of SE the K30-K33 is more appropriate
Conversation about hum, buzz and the like.
Hello All,
Thanks for all this conversation about hum, buzz and the like.
First, Pete Millett indicates that this amplifier design should be placed into a grounded metal enclosure.
Second, this particular amplifier is built into a wooden box that does not shield the amplifier. In this thread the effort is to minimize the hum and or buzz without a shielded enclosure. Seems to me to be a good idea to minimize hum and buzz by layout, conductor routing and all the usual suspects.
Lately I have been bread boarding an assortment of tube circuits on the bench. There is always the power series of 60 hz, 120 hz, 180 hz, 240 hz 300 hz peaks on the FFT. The FFT scans have been done with all the parts and test leads loose on the bench top. Carefully arranging the parts and test leads sometimes lowers the power harmonic series. Even with all the power supplies switched off the power series often are still prominent in the FFT scan.
For grins today I placed the parts, pieces and test leads in a grounded (steel) NEMA 3R rain tight enclosure. The 60 hz peak on the FFT scan was reduced about 10 - 12 dB’s, the higher harmonics were not reduced as much.
An added note; the power coming into you lab is unlikely a perfect 60 or 50 hz. There is commonly 120 hz, 180 hz, 240 hz 300 hz distortion present in your supplied power.
DT
Hello All,
Thanks for all this conversation about hum, buzz and the like.
First, Pete Millett indicates that this amplifier design should be placed into a grounded metal enclosure.
Second, this particular amplifier is built into a wooden box that does not shield the amplifier. In this thread the effort is to minimize the hum and or buzz without a shielded enclosure. Seems to me to be a good idea to minimize hum and buzz by layout, conductor routing and all the usual suspects.
Lately I have been bread boarding an assortment of tube circuits on the bench. There is always the power series of 60 hz, 120 hz, 180 hz, 240 hz 300 hz peaks on the FFT. The FFT scans have been done with all the parts and test leads loose on the bench top. Carefully arranging the parts and test leads sometimes lowers the power harmonic series. Even with all the power supplies switched off the power series often are still prominent in the FFT scan.
For grins today I placed the parts, pieces and test leads in a grounded (steel) NEMA 3R rain tight enclosure. The 60 hz peak on the FFT scan was reduced about 10 - 12 dB’s, the higher harmonics were not reduced as much.
An added note; the power coming into you lab is unlikely a perfect 60 or 50 hz. There is commonly 120 hz, 180 hz, 240 hz 300 hz distortion present in your supplied power.
DT
Grounded metal enclosure, because it is open for courious nosy hands!
The hum I am adventuring is not because of the wooden box (I have a aluminum plate now 🙂)
Negative adventure continues... but ! the hum is not present at beginning... now only after 5 sec... crescendo... hum...
The hum I am adventuring is not because of the wooden box (I have a aluminum plate now 🙂)
Negative adventure continues... but ! the hum is not present at beginning... now only after 5 sec... crescendo... hum...
tracer
Hi there h: Following your hum adventure daily. "Back in the day", tube days for me was 1956-71, we used a signal tracer to observe any point on a tube circuit. The tracer consisted of a 600v non polarized capacitor of about o.o1uf connected thru a lead to another amplifier's line input and a ground lead with an alligator clip. Use a short piece of insulation on the capacitor lead, sort of like a meter probe. Using this to trace back from the out put you may be able to trace the hum back to its source, DIY 1950's. Note there was a self contained commercial version of the signal tracer, that we sold at the electronics wholesaler where I worked. ... regards, Michael
Hi there h: Following your hum adventure daily. "Back in the day", tube days for me was 1956-71, we used a signal tracer to observe any point on a tube circuit. The tracer consisted of a 600v non polarized capacitor of about o.o1uf connected thru a lead to another amplifier's line input and a ground lead with an alligator clip. Use a short piece of insulation on the capacitor lead, sort of like a meter probe. Using this to trace back from the out put you may be able to trace the hum back to its source, DIY 1950's. Note there was a self contained commercial version of the signal tracer, that we sold at the electronics wholesaler where I worked. ... regards, Michael
Very interested in trying this project. Does anyone have the dimensions of the PCB? If building one's own chassis, to accommodate the board, one would need to mount it on standoffs from the top panel. Is that right?
Yes that's correct. I like Pete Millett boards because he puts the components on one side and the tubes on the other side. That makes so much sense, it's a shame so few other tube amp boards do it that way. Heat sinks and tubes belong on one side components on the other. This little detail allows you to poke the tubes and heat sinks through the top. The shoulders on the sockets will make it look like it's really chassis mounted. As a precaution it's good to put a sheet of insulator between board and chassis. Board mounts on standoffs exactly the height where the tube socket shoulders contact the metal chassis.
I have been breadboarding this amp for a junk box project just this week, not with the PC board though. I have a closet full of Compactrons I need to use in my lifetime!
I have been breadboarding this amp for a junk box project just this week, not with the PC board though. I have a closet full of Compactrons I need to use in my lifetime!
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