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Old 28th June 2020, 12:03 AM   #801
carlman14 is offline carlman14  United States
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Quote:
Originally Posted by vernonb View Post
If you haven’t done the non-standard layout in post 747 I haven’t a clue I’m afraid

Perhaps some pics would help?

I ended up sticking with the standard layout. So all the tubes are where they're supposed to be. Here's some pics (shown is the standard CLC filter iteration with auxiliary cap):
IMG_20200627_165112.jpg

IMG_20200627_165120.jpg

IMG_20200627_165133.jpg

IMG_20200627_165155.jpg

IMG_20200627_165310.jpg


I'll read that article you sent and see if it gives me any ideas.
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Old 28th June 2020, 01:26 AM   #802
Tubelab_com is offline Tubelab_com  United States
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Did you switch out the 5842 tubes?
Try the amp without the 5842's. If the hum remains, they are not the problem.

It is possible that the filament regulator is on the edge of dropout, especially if your line voltage is on the low side. How much voltage do you have across C1, C12 or C13 (they are all in parallel).
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Old 28th June 2020, 03:30 AM   #803
carlman14 is offline carlman14  United States
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Originally Posted by Tubelab_com View Post
Try the amp without the 5842's. If the hum remains, they are not the problem.

It is possible that the filament regulator is on the edge of dropout, especially if your line voltage is on the low side. How much voltage do you have across C1, C12 or C13 (they are all in parallel).

The hum is still there with the 5842's unplugged. So we can rule those out.


The voltage across C12 is 3.68V, and my line voltage is 124V AC.
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Old 28th June 2020, 11:34 AM   #804
pieroh is offline pieroh  Germany
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Quote:
Originally Posted by Tubelab_com View Post
Try the amp without the 5842's. If the hum remains, they are not the problem.

It is possible that the filament regulator is on the edge of dropout, especially if your line voltage is on the low side. How much voltage do you have across C1, C12 or C13 (they are all in parallel).
Hi,
I'm also experiencing hum, in dependence of the line votlage. When the line voltage is on the low side, there is hum, if the line voltage is at its max. (230 V here in Germany) there is no hum.
It seems like what George is pointing out.
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Old 29th June 2020, 10:57 AM   #805
Tubelab_com is offline Tubelab_com  United States
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In the case of dropout related issues on the filament regulator the situation can usually be improved by adding capacitance in parallel with C1, C12 or C13.

The 1N5401 diodes can be swapped for Schottky diodes if you are running 5 volts tubes. They are not in the filament circuit when using 2.5 volt tubes.

The Sharp regulator in the original TSE was the lowest dropout regulator on the planet when I designed the TSE. Unfortunately it is extinct.

When designing the TSE-II I tested everything available through distribution that had similar dropout specs in the circuit with 2A3's (worst case 5 volt 5 amp draw for two tubes) at low line voltages. The Microchip part was clean to 108 volts into a 120 volt transformer when running 2A3's. I could get that down to 105 volts with about 100,000 uF of total capacitance on the regulator input (C1). Only minimal improvements were seen above 100,000 uF. This must be a low ESR cap.

Dropout should only be an issue when low line voltage, high current demand from the regulator (2A3's) and a power transformer that delivers less than 6.3 volts under the load current drawn.
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Old 29th June 2020, 11:14 AM   #806
pieroh is offline pieroh  Germany
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Many thanks George!
I will increase the capacity at the input of the regulator.

Cheers
Peter
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Old 29th June 2020, 10:26 PM   #807
carlman14 is offline carlman14  United States
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I think I figured out the source of my hum! Look at these excerpts I found:

1. Quote from a Lundahl PT page: https://www.lundahltransformers.com/...heets/1683.pdf --- "Output current from rectifier: 63% of above with cap. input rectifier, 95% of above with choke input rectifier."

2. Quote from the EML 5U4G page: 5U4G Emission Labs Data Sheet --- "The much more gentle L-C circuit. can load a mains transformer up to 100% of it's specified ratings, wheras C-L-C circuits can load a transformer only up to 66% (or the transformer will produce audible hum + magnetic hum field)".

According to these, the available current of my PT with a cap input rectifier is 63-66% of it's actual rating, or 130mA*0.66 at the most, which is 85.8 mA. That is not enough for the ~100mA requirement of the 45 amp. It occurred to me that I've never listened to the amp with the bias turned down on the 45's. I turned down the bias while wearing my headphones (therefore lessening the mA draw on PT), and sure enough, the hum gradually went away as the bias was turned down. So I think this means I am pulling more current than what's allowed by my transformer in a cap input rectifier PSU.

Considering that nobody complains about this kind of hum with speakers (which would have more conventional 5k8 OPTs, which would reduce hum further), I imagine this deficiency in PT amperage is not noticeable on lower sensitivity output. Confirmed this on my arya, which has a lower sensitivity. The hum was inaudible with those headphones at normal bias.

Does this explanation sound plausible? If so, it seems the solution is to simply buy a PT with a higher mA rating (maybe 160mA or higher).
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Old 30th June 2020, 01:02 AM   #808
Tubelab_com is offline Tubelab_com  United States
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Quote:
Does this explanation sound plausible?
It is true that you should load a transformer somewhere between half and two-thirds of it's rating when it is running into a capacitor input filter.

Remember the filament supply is also running into a cap input filter. You made several changes in your B+ and B- supplies and these had no effect. This would indicate that the problem lies elsewhere. If you can find a big cap to add across C1, try it to see if it has any effect.

I am using a Hammond transformer with a 6 amp rating for the 6.3 volt winding. I can connect my 32 ohm headphones directly to the speaker terminals and not hear any hum, and I'm running 2A3's. Hammonds are known for producing more voltage than they are rated for.

I have used Transcendar OPT's and like them. I have never tried their power transformers and do not know how much voltage they actually deliver under load. The changing load on the B+ supply when you adjust the bias may affect the voltage on the 6.3 volt winding slightly.
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Old 30th June 2020, 01:25 AM   #809
carlman14 is offline carlman14  United States
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Quote:
Originally Posted by Tubelab_com View Post
Remember the filament supply is also running into a cap input filter. You made several changes in your B+ and B- supplies and these had no effect. This would indicate that the problem lies elsewhere. If you can find a big cap to add across C1, try it to see if it has any effect.

Thanks for the input. Almost all of my B+ configurations had low enough ripple to not have hum. So I figured that if there was no difference in hum from the B+ changes, it might be my PT complaining about having too much current drawn from it.


Just for the sake of trying everything, will try both a different PT (Hammond 370FX probably) as well as a cap across C1. Would this cap work: ESMH160VSN104MA80T United Chemi-Con | Mouser
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Old 1st July 2020, 03:06 PM   #810
pieroh is offline pieroh  Germany
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Quote:
Originally Posted by Tubelab_com View Post
In the case of dropout related issues on the filament regulator the situation can usually be improved by adding capacitance in parallel with C1, C12 or C13.

The 1N5401 diodes can be swapped for Schottky diodes if you are running 5 volts tubes. They are not in the filament circuit when using 2.5 volt tubes.

The Sharp regulator in the original TSE was the lowest dropout regulator on the planet when I designed the TSE. Unfortunately it is extinct.

When designing the TSE-II I tested everything available through distribution that had similar dropout specs in the circuit with 2A3's (worst case 5 volt 5 amp draw for two tubes) at low line voltages. The Microchip part was clean to 108 volts into a 120 volt transformer when running 2A3's. I could get that down to 105 volts with about 100,000 uF of total capacitance on the regulator input (C1). Only minimal improvements were seen above 100,000 uF. This must be a low ESR cap.

Dropout should only be an issue when low line voltage, high current demand from the regulator (2A3's) and a power transformer that delivers less than 6.3 volts under the load current drawn.
I added another capacitor of 47.000 F at the input of the regulator.....and now my TSE-II is dead silent!
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