Hi, I have a pair of interstage transformers in my monoblocks. One of the ITs has a mechanical hum (audible from the listening position and a real PIA) and the other does not hum. The ITs seem to perform the same, other than the pesky mechanical hum. BTW: No hum from either speaker, so its no in the signal. Any thoughts on where to begin to debug this? Thanks, Pat
Please attach pics. If they have screws at the corners, surely adjusting them will solve the problem. If they are potted, you will need to dissolve the potting material which posibbly damages the windings.
An option may be include them in a box and fill it with acoustical adsorvent material.
An option may be include them in a box and fill it with acoustical adsorvent material.
Hi Andy, I have a note out to Yves at Monolith on this regard. TBD. I was hoping that it was something I could do instead of shipping to/from US/Europe.
Hum?
What kind of Hum?
As in 50Hz, 60Hz, 100Hz, or 120Hz?
Are you using a Magnetic Steel Chassis?
Power transformers and filter chokes put powerful magnetic fields onto the steel chassis.
Then, any magnetic material, like the potting and laminations of an interstage transformer that is not tightly attached to the chassis will Hum.
Or Hum as when you hear music coming from the Interstage transformer?
Please be more specific.
What kind of Hum?
As in 50Hz, 60Hz, 100Hz, or 120Hz?
Are you using a Magnetic Steel Chassis?
Power transformers and filter chokes put powerful magnetic fields onto the steel chassis.
Then, any magnetic material, like the potting and laminations of an interstage transformer that is not tightly attached to the chassis will Hum.
Or Hum as when you hear music coming from the Interstage transformer?
Please be more specific.
6A3, there is no hum from the speakers. Its a mechanical hum from the IT. 120hz hum. The IT is potted in a metal chassis which is metal screwed to the amp chassis which is grounded. I don't know if the IT metal chassis is magnetic.
The Power Transformer is on the Top of the chassis. The chokes are next to the IT below the chassis. There is a 3/8" steel plate for the top of the chassis. See attached.
The Power Transformer is on the Top of the chassis. The chokes are next to the IT below the chassis. There is a 3/8" steel plate for the top of the chassis. See attached.
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banpuku,
Reduce the hum . . .
Use some Aluminum spacers between the interstage and the chassis.
Use some Aluminum spacers between the choke and the chassis.
1/4 inch spacers should help (about 6mm or more).
Be sure to use Brass screws. Do Not use Steel screws to mount the interstage and choke.
Get a magnet.
Even one of those magnetic stick-on refrigerator advertisements.
Use the magnet to discover if the interstage Potting is Magnetic Steel, or not.
The laminations inside the Interstage are magnetic.
Reduce the hum . . .
Use some Aluminum spacers between the interstage and the chassis.
Use some Aluminum spacers between the choke and the chassis.
1/4 inch spacers should help (about 6mm or more).
Be sure to use Brass screws. Do Not use Steel screws to mount the interstage and choke.
Get a magnet.
Even one of those magnetic stick-on refrigerator advertisements.
Use the magnet to discover if the interstage Potting is Magnetic Steel, or not.
The laminations inside the Interstage are magnetic.
It certainly is magnetic. I am going to use some blue vibration isolation grommets. This addresses the effect, but not the root cause.
Update: So I pulled out my stethoscope and put it on the IT. Very little hum. So, where was the hum emanating? The Filament Transformer. So, I re-tightened all the screws on the FT / chassis and sure enough, that helped significantly. The FT is still humming, but nowhere nearly as audible as before.
Can you put here PSU schema for 866? I want to use to my 2A3 SE parallel amplifier. Which are the downsides of 866? Thank you!
klauss00 this is the schematic from about 3 weeks ago. I have changed the driver, but the 866A PS is still the same. Voltage might be off a bit, but it should serve the purpose. When using the 866 (or any mercury rectifiers), please follow these rules:
1. provide a separate power switch that toggles the AC voltage (on or off) for the rectifiers. The power switch should also provide the AC to a separate B+ power switch. This solution ensures that B+ will only be available if the filaments are heated.
2. pre-heat the rectifiers for 1-2 hours upon first time usage. Do NOT apply B+ for at least 1-2 hours. Thereafter, pre-heat rectifiers for about 1 minute prior to applying B+
The 866A is a great rectifier if used with care.
1. provide a separate power switch that toggles the AC voltage (on or off) for the rectifiers. The power switch should also provide the AC to a separate B+ power switch. This solution ensures that B+ will only be available if the filaments are heated.
2. pre-heat the rectifiers for 1-2 hours upon first time usage. Do NOT apply B+ for at least 1-2 hours. Thereafter, pre-heat rectifiers for about 1 minute prior to applying B+
The 866A is a great rectifier if used with care.
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What about RF noise? It is the belief that mercury rectifier are prone to RF noise and in order to cancel it you need to put a RF choke in series with each plate (for type 82 and 83)
Did you measure voltage drop for each plate? less voltage drop less sag
Did you measure voltage drop for each plate? less voltage drop less sag
What about Mercury Rectifiers and power interruptions?
The amplifier is warmed up and playing.
The power company temporarily drops the power on your street (no power).
All the switches on your amplifiers are already on (you did not get across the room to turn them off).
Then the power comes on again. The mercury rectifiers are cold, but the B+ switch is on.
Ouch!
Good Luck
If you want a pretty tube on your amplifier?
Just connect a dropping resistor to B+, and the other end to an OD3 to ground.
Pass 7 mA through the OD3 tube.
Example: with 300V B+, 150V at 7mA through the series resistor, 150V from the other end of the resistor to the OD3 (150V across the OD3).
150V / 0.007A = 21.5k
Use a 20k 5 Watt dropping resistor from 300V B+ to the OD3 to ground.
With B+ that is not 300V, use a resistor that drops the B+ voltage down to 150V.
350V - 150V OD3 = 200V across the resistor. 200V / 0.007A = 28.6k Use a 30k 5 Watt resistor
The amplifier is warmed up and playing.
The power company temporarily drops the power on your street (no power).
All the switches on your amplifiers are already on (you did not get across the room to turn them off).
Then the power comes on again. The mercury rectifiers are cold, but the B+ switch is on.
Ouch!
Good Luck
If you want a pretty tube on your amplifier?
Just connect a dropping resistor to B+, and the other end to an OD3 to ground.
Pass 7 mA through the OD3 tube.
Example: with 300V B+, 150V at 7mA through the series resistor, 150V from the other end of the resistor to the OD3 (150V across the OD3).
150V / 0.007A = 21.5k
Use a 20k 5 Watt dropping resistor from 300V B+ to the OD3 to ground.
With B+ that is not 300V, use a resistor that drops the B+ voltage down to 150V.
350V - 150V OD3 = 200V across the resistor. 200V / 0.007A = 28.6k Use a 30k 5 Watt resistor
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6A3sUMMER, in my opinion the big advantage of mercury rectifier it is represented by the constant V drop regardless current flow. And power interruption, use a relay in order to delay plate voltage for rectifier as Peter Millett used in his "Unnecessarily Complex 300B amp"
Yes, I use a delay for B+. RF noise has not been an issue for me. So, I have no experience with RF Choke.
1. Many users of Mercury Rectifiers do not use any relay; they pay no attention to Hot Start, Power interruptions, and other considerations of using such rectifiers.
2. Solid state diodes have the least voltage drop of all rectifiers.
Their delta voltage with delta current demands is less than any other rectifiers.
All other factors being equal, solid state has the most steady B+ voltage (other than very stiff voltage regulators).
3. Various mercury rectifiers and circuits do not generate much RF; other mercury rectifiers do generate a lot of RF.
Some amplifiers may be affected by that RF, other amplifiers may not.
But many AM and Shortwave radios are affected by the RF of some of those mercury rectifier circuits.
4. Some amplifier circuits that use delayed B+ do have transients going to the speakers; others do not have transients when the delayed B+ turns on.
Some amplifiers use a muting circuit to prevent the transient to the loudspeaker.
Please be aware of these tradeoffs.
I am just saying.
2. Solid state diodes have the least voltage drop of all rectifiers.
Their delta voltage with delta current demands is less than any other rectifiers.
All other factors being equal, solid state has the most steady B+ voltage (other than very stiff voltage regulators).
3. Various mercury rectifiers and circuits do not generate much RF; other mercury rectifiers do generate a lot of RF.
Some amplifiers may be affected by that RF, other amplifiers may not.
But many AM and Shortwave radios are affected by the RF of some of those mercury rectifier circuits.
4. Some amplifier circuits that use delayed B+ do have transients going to the speakers; others do not have transients when the delayed B+ turns on.
Some amplifiers use a muting circuit to prevent the transient to the loudspeaker.
Please be aware of these tradeoffs.
I am just saying.
banpuku,
Mechanical Hum:
Some chokes hum because they are on a magnetic steel chassis.
Some chokes hum on their own.
Some chokes do Both.
I hope you solve the mechanical hum issue.
Mechanical Hum:
Some chokes hum because they are on a magnetic steel chassis.
Some chokes hum on their own.
Some chokes do Both.
I hope you solve the mechanical hum issue.
Today I inserted some vibration isolation grommets (the blue ones that you can get at mcmaster). They did reduce the vibration that was then being amplified by the top chassis plate. So, the mechanical hum is no longer audible at the listening position. There is still a slight mechanical buzz generated by the filament transformers, but the grommets have minimized its impact. This is a huge relief because I can no longer hear any buzz/hum unless I put my ear up near the filament transformer. Thanks for those that helped.