Placing_5Y3GT_of_Champ_5F1_into_STANDBY

[hewo]

Is it electrically safe to power up only the heaters of the 5Y3GT, 12AX7B, and 6V6GT ?
I have not energized anything yet but already built it this way using a DPTT (330-NONE-300) to feed HT_AC (both leads) to the 5Y3GT. The HT_AC windings are CT earthed.
I am concerned because the 5Y3GT heater is NOT isolated, meaning one of its heater pins is connected to the highest DC condenser. This condenser NEVER gets to see the opposing 5VAC leg that is connected to the other 5Y3GT heater pin. Did Fender ever standby the 5Y3GT ? Legacy schematics always show STANDBY open circuiting HT_DC, meaning the 5Y3GT is ALIVE producing DC. I don't know for certain whether there will be any detriment, undesired transient, unnecessary wear tear stressors, by open circuiting both leads of the HT_AC windings feeding the 5Y3GT

another concern is whether or not it is electrically safe to install protection contingency HT_DIODES (two of them in series) downstrm of the 5Y3GT output feeding the highest condenser.

final concern is whether to install switchable SOLIDSTATE VERSUS 5Y3GT rectification to feed the highest condenser. some say the efficiency of solidstate diodes are excessive resulting in higher HT_DC that will accelerate CLASS A wear and tear because of greater current flow.

it is troubling trying to obtain a 4 ohm paper spkr that is very sensitive (spl). electrovoice has 110dB but its upper register of frequencies suffers (desired: 7.5K reach). the only alternative i can think of is to invest in a quality OT capable of 16_8_4 selectable. but it's much easier to just get a 4 ohm spkr that's very sensitive.

[Enzo]

Fender Champs have been playing now for maybe 60 years, I don't think at this late date we need to start worrying that their design is defective.

The Champ has absolutely no need of a standby switch, in fact MOST amps do not need such a switch. If you want one anyway, then go ahead and add one. There are certainly MANY MANY amps with standby switches, and none of them blow anything up for having one, yes, including amps using rectifier tubes. Of course you can power up the heaters alone with nothing else powered, it is done every day.

I would quibble with your terms a little. The 5VAC winding is indeed isolated, it has no connection to ground or the other heaters. That isolation is the REASON it can be connected to high voltage. In the 5Y3, the heater IS the cathode, so there is no way to avoid the heater being at B+ voltage, that is how they all spend their lives. The 5VAC flowing THROUGH the tube heater is what makes the cathdode emit electrons, it doesn't matter that one point along the 5v circuit is connected to B+. Think of the high tension power lines in your town. Now think about little birds that go up and sit on those wiresw, even though there are thousands of volts in them. The reason the birds survive is that the birds are not grounded. They can attach themselves to the wire because they are connewted to nothing else. Your 5VAC is connected to nothing else but that high voltage circuit.

You want to put diodes AFTER the rectifier tube? OK, can;t hurt anything, but what would the purpose be? What would it DO? If you want to protect something, put one diode in series with each AC wire going to pins 4 and 6 of the tube socket. That will protect your caps and circuits from a shorted 5Y3, which is FAR more likely than anything else there.

5Y3 tubes do indeed drop voltage across themselves, so if you replace a tube with a silicon diode pair, yes, you B+ will rise considerably. This is a class A amp, so the current draw is very steady, there won't be any sag from B+ draw.

WHy do you need 7.5kHz response in a guitar amp? That is much higher than most.

110db is pretty darn efficiant for a speaker. CHamps are generally used in close situations, not filling concert halls, so the difference in loudness between 5 watts and 20 watts is not large - about 6db if all else is equal.

[hewo]

Thankyou Enzo,
1. standby would be fruitful if the selectable rectification mode is employed.
2. caution: pure diode rectification will elevate the htac (300/330 selectable) to dc voltages that may risk damaging (the ot from excessive dc flow?) ?
3. half-wave rectification would yield a multiplier of 1.4 onto the selected htac (330/300 selectable, CT earthed), that is pretty hefty?

[Enzo]

If you switch from tube to silicon rectification your B+ will go up a few tens of volts. The transformer is the last thing I;d worry about. You might find tubes objecting to higher voltage, and depending on the caps you have, the caps may find their voltage ratings challenged. The transformer won;t care.


Half wave or full wave - either one rectifies and filters to the peak voltage of the AC waveform.

[hewo]

Thankyou Enzo for your responses

If you switch from tube to silicon rectification your B+ will go up a few tens of volts. The transformer is the last thing I;d worry about. You might find tubes objecting to higher voltage, and depending on the caps you have, the caps may find their voltage ratings challenged. The transformer won;t care.


Half wave or full wave - either one rectifies and filters to the peak voltage of the AC waveform.

Wasn't the thumb rule (actually calculus integration of the sine wave) yields root of two divided by two, as the magic multiplier for diode rectification. I vaguely recall that number as 1.414 or something similar (college was in 79). if this is so, wow! ht_dc will be unmanageably large! and to lower it, energy will be wasted in heat. the chinese 5F1 kit provided 450WVDC: 16uF node one, 8uF node two, 8uF node three, and 2watt voltage reducing resistors. forum commentary isolates prone suspects of catastrophic failure (from diode rectification): present day factory tubes from the shuguang factory have mortality statistics i know not of.

[Enzo]

Peak voltage of a sine wave is 1.414 times its RMS voltage, or if you prefer, RMS is 0.707 times peak.

When you rectify AC, you then have pulsing DC, and it still has the same peak voltage. When you add the filter cap, then it charges up to the peak voltage. Full wave or half wave. 300vRMS of AC will rectify and filter to 424vDC. 330vAC becomes 466vDC.

[hewo]

Possible_Over_Voltage_Condition_5F1_Kit

Peak voltage of a sine wave is 1.414 times its RMS voltage, or if you prefer, RMS is 0.707 times peak.

When you rectify AC, you then have pulsing DC, and it still has the same peak voltage. When you add the filter cap, then it charges up to the peak voltage. Full wave or half wave. 300vRMS of AC will rectify and filter to 424vDC. 330vAC becomes 466vDC.

Thankyou Enzo for your responses:
1. This is bad news isn't it? With that large DC, the 6V6GT will be on threshold of burnthrough won't it?
2. 5F1 voltages from fender's original schematic show markedly lower voltages don't they?
3. plate powering condenser caps all rated 450wvdc but 466 is over that!
4. should the htac selectable DPTT (center-off) for 330/300 htac be abandoned altogether because of the overvoltage condition?

[Enzo]

SIlicon diodes only drop a volt or less when rectifying, so that 300AC to 424DC is a theoretcial number ignoring any other factors. Tube rectifiers by their nature drop voltage across themselves, so 300VAC into a 5Y3 will result in lower voltages on the DC side that with silicon diodes.

50 year old schematics also were often drawn for mains voltages closer to 110vAC rather than roday's 120-125v. Adding 10-15v on the primary side will result in 25-30vDC higher on the secondary side.

If your transformer runs with selectable 300vac or 330vac, then select the lower voltage and don't use the higher. Or indeed use a different transformer.

[hewo]

Thankyou Enzo for your responses

SIlicon diodes only drop a volt or less when rectifying, so that 300AC to 424DC is a theoretcial number ignoring any other factors. Tube rectifiers by their nature drop voltage across themselves, so 300VAC into a 5Y3 will result in lower voltages on the DC side that with silicon diodes.

50 year old schematics also were often drawn for mains voltages closer to 110vAC rather than roday's 120-125v. Adding 10-15v on the primary side will result in 25-30vDC higher on the secondary side.

If your transformer runs with selectable 300vac or 330vac, then select the lower voltage and don't use the higher. Or indeed use a different transformer.

I energized/measured for the 1st time this morn but did not switch htac into 5Y3GT: with respect to earth, 3.33vac measured on each heater leg (CT earthed), 120vac measured on utility line side, 303.4vac measured on each 300htac leg, 5.4vac measured across 5Y3GT's heater legs, and 333.4vac measured on each 330htac leg. all of the chinese kit shuguang provided tubes were installed and confirmation of heaters glow affirmed.

but I did not want to apply htac into 5Y3GT just yet. i would like to first bring up utility ac through a variac but this corrupts adequacy of heater energies so I don't truly understand how bringing up utility ac slowly prior to engaging htac into the 5Y3GT is going to benefit. please assist on sequencing this gradual variac approach esp on engaging htac into the 5Y3GT

Is the 330htac capability useless for 6V6GT operation? or is this only detrimental for shuguang 6V6GT and/or shuguang 5Y3GT?
If useless, maybe the PT can accomodate single ended EL34 operation instead? do folks do this or is adjustment circuitry accomodation too much humbug?