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    5V AC Filiment Voltage On Amp With Solid State Rectifier

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    mazeeff

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    5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by mazeeff on Tue Jan 08, 2019 6:48 am

    I have a VTA-120 with a Weber solid state rectifier. In looking at the schematic, I noticed that the 5V AC filament voltage is connected directly to the Cathode output, of the 5AR4 rectifier. I suspect that this small AC signal is then filtered out by the following filter Capacitance. For those of us utilizing a solid state rectifier, is there any benefit to removing the 5V AC from the circuit, simply to reduce unnecessary filtering? I never plan to use a tube rectifier in the future!

    Mike
    peterh
    peterh

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by peterh on Tue Jan 08, 2019 6:58 am

    mazeeff wrote:I have a VTA-120 with a Weber solid state rectifier. In looking at the schematic, I noticed that the 5V AC filament voltage is connected directly to the Cathode output, of the 5AR4 rectifier. I suspect that this small AC signal is then filtered out by the following filter Capacitance. For those of us utilizing a solid state rectifier, is there any benefit to removing the 5V AC from the circuit, simply to reduce unnecessary filtering? I never plan to use a tube rectifier in the future!

    Mike
    Yes.
    Removing the 5V from the B+ chain reduces the possible failure modes.
    In addition this winding may have another use, connected in series with the
    primary it will reduce or increase the incoming voltage with 5V if you have that need.
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    mazeeff

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by mazeeff on Tue Jan 08, 2019 7:09 am

    Thanks Peter. I will remove the circuit. I never thought about using it as a "Bucker". Good idea!

    Mike
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    StevieRay

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by StevieRay on Wed Jan 09, 2019 9:23 am

    I'm using a Weber WS-1 w/thermistor (built-in) SS rectifier, and don't ever intend to use a tube rectifier.

    Since my line voltage varies from 120-123, I long ago decided to use some sort of 'bucker' or variac when I built my ST-120.

    when I finally pulled the trigger and bought one (still only ~100 hours on the tubes), I used that rectifier 5V filament winding as a bucking winding -- enjoying 115-118vac  on the input winding of the power transformer and never have to worry about it again, or lug a variac around, etc.

    And it's all reversible if I lose my mind and ever buy a super huge space heater GZ37 tube rectifier!
    erhard-audio
    erhard-audio

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by erhard-audio on Wed Jan 09, 2019 11:33 am

    it is important to note, if you are going down the solid state rectification road on your amp, that 5VAC winding will no longer be used at all, this excludes the Weber rectifier!
    I have not used tube rectification in my builds for years now, just two diodes. That allowed me to eliminate the 5VAC winding as well as lowering the high voltage secondary level (virtually no voltage drop across diodes) in the power transformers I use, which are custom made for me.
    This of course then brings up one warning. If you do decide to go solid state using diodes (not the Weber rectifier) and due to the fact that the voltage drop across a diode is almost nix when compared to a tube rectifier, your B+ will now of course be higher as well!
    You can control that, up to a point, by increasing the value of the dropping resistor in the power supply and maybe even the resistors wattage.
    So you MUST keep that in mind when going solid state using diodes.
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    mazeeff

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by mazeeff on Wed Jan 09, 2019 11:38 am

    Thanks for the feedback. I use SS rectification in all three of my tube amps, and use an external variac on all three. This allows me some flexibility in adjusting the final B+ voltages, regardless of rectification.

    Mike
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    StevieRay

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by StevieRay on Wed Jan 09, 2019 1:06 pm

    The Weber WS-1 has NO dropping resistor to simulate a tube rectifier voltage drop like the WS68 and others.  I suppose just some doides solderred in would do the same.

    However, the model of the WS-1 I have includes a thermistor to help reduce inrush on turn-on.  I also use the time-delay relay (TDR) with my ST-120.

    Does the therrmistor drop any voltage ?  I haven't measured, but if any, probably not much.

    But even using a SS rectifier, and a nice steady diet of 115-118 input volt from 'bucking' winding, ALL of my internal voltages -- B+, fllament, etc. -- are in the middle of the range.

    Now if my line voltage (not using the bucker) were higher, like say 122-123, then using the SS recitifier may result in too much B+ (bad for the quad cap).

    But if your line input is 115-118vac I see no need in the WS68 or other Webers that waste heat/energy/blah through a silly resistor that may fail one day because it's wrapped in that copper coffin and can't dissipate the heat.
    erhard-audio
    erhard-audio

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    Re: 5V AC Filiment Voltage On Amp With Solid State Rectifier

    Post by erhard-audio on Wed Jan 09, 2019 1:26 pm

    StevieRay wrote:The Weber WS-1 has NO dropping resistor to simulate a tube rectifier voltage drop like the WS68 and others.  I suppose just some doides solderred in would do the same.

    However, the model of the WS-1 I have includes a thermistor to help reduce inrush on turn-on.  I also use the time-delay relay (TDR) with my ST-120.

    Does the therrmistor drop any voltage ?  I haven't measured, but if any, probably not much.

    But even using a SS rectifier, and a nice steady diet of 115-118 input volt from 'bucking' winding, ALL of my internal voltages -- B+, fllament, etc. -- are in the middle of the range.

    Now if my line voltage (not using the bucker) were higher, like say 122-123, then using the SS recitifier may result in too much B+ (bad for the quad cap).

    But if your line input is 115-118vac I see no need in the WS68 or other Webers that waste heat/energy/blah through a silly resistor that may fail one day because it's wrapped in that copper coffin and can't dissipate the heat.

    Yes, a good point regarding the thermistor, I use one in ALL my builds.
    One can 'regulate' B+ by increasing the dropping resistor, that of course would be a permanent adjustment of B+ and will still follow the incoming mains supply variations. But if your household has a fairly steady supply level, then adjusting the dropping resistor to a slightly higher value is about all that would be required.
    Here is a web page that will calculate the required dropping resistor value and wattage, but you still need to know the start/raw B+ level, the desired B+ level and the current draw of B+.
    http://www.gtsparkplugs.com/Dropping_Resistor_Calc.html

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