open ckt idling high tension pt ac detrimental?

[hewo]

is it ok to open ckt pt ht ac while htrs are warming?

Or is it necessary to slightly load ht ac while htrs warm ckt 5f1?

If htrs are consuming energy during htr warming, does this pt load alone maintain sufficient throughput through pt to keep pt from idling without detrimental effect?

I say this because idling a completely unloaded secondary (plural) of a pt is unhealthy because of pt internal materials irreversibilities

[Enzo]

I say this because idling a completely unloaded secondary (plural) of a pt is unhealthy because of pt internal materials irreversibilities

Never heard this, please explain how that would happen. There is no DC to try to magnetize the core metal.

is it ok to open ckt pt ht ac while htrs are warming?

Certainly, why wouldn't it be? It is done all the time. Like these Marshalls
http://bmamps.com/Schematics/marshal..._year_1988.gif
http://bmamps.com/Schematics/marshal...2-100-iss1.pdf

Do I correctly understand you are making a Champ with a standby switch?

[hewo]

Hi enzo and thanks for assist.

Chromed heavy gage chassis build diy 5f1 china kit year built 2010 with amendments, mv, hi-pass cap 220 on both 1meg audio pots, 1k 6v6 grid stopper, 1meg ground bridge resistor on 1meg mv, disengage nfb switch, secondary pt ht taps of 300/330 ac switchable via dpdt center off, utilizing both ac wires of each ht output ac taps.
My question concerns electrifying pt with only load being drawn through it is htrs, 5y3, ecc83, 6v6.

Realize most standbys feed all the way through dc master electrolytic and ballast bleed resistor there to earth, and there is the gate to switch feed to the ot and tributaries ahead.

[Enzo]

True, most standbys use the common switch in the DC lead, but Marshall is one notable who did it on the AC side, as did some others. Other designers don't mess with the power supply and shunt the signal path.

[R.G.]

My question is why would you ever think that running the amp with the HV outputs from the PT *would* or *could* hurt the PT or anything else in the amp.

Line transformers are fine with no load at all. In that case, they just act like inductors across the AC line. A PT with only heaters loading it is fine. There is no detrimental effect on the PT from idling without any load at all, or with a tiny load, or all the way up to full load.

I'm very interested in how you got the idea that the PT could possibly be hurt by this.

[pdf64]

My question is why would you ever think that running the amp with the HV outputs from the PT *would* or *could* hurt the PT or anything else in the amp.

Line transformers are fine with no load at all. In that case, they just act like inductors across the AC line. A PT with only heaters loading it is fine. There is no detrimental effect on the PT from idling without any load at all, or with a tiny load, or all the way up to full load.

I'm very interested in how you got the idea that the PT could possibly be hurt by this.

Maybe hewo is thinking that it works in a similar way to running the OT without the normal secondary load, which could be a bad thing?

I wonder why kit providers / buyers perceive that adding standby is a greater benefit than adding secondary fusing of some / any sort?

[hewo]

primary windings pt energized but no drawing of energy from secondary winding (s)

If no energy is drawn out from pt secondary winding (s) the primary winding becomes a mere coil load to the utility company's feed of line power.

Think of the tungsten filament heating inside incandescent bulb fed by utility company ac feed.

So I think the weak link is the primary winding, as it appears just like said tungsten filament, only less resistive being copper filament

My question is why would you ever think that running the amp with the HV outputs from the PT *would* or *could* hurt the PT or anything else in the amp.

Line transformers are fine with no load at all. In that case, they just act like inductors across the AC line. A PT with only heaters loading it is fine. There is no detrimental effect on the PT from idling without any load at all, or with a tiny load, or all the way up to full load.

I'm very interested in how you got the idea that the PT could possibly be hurt by this.

[hewo]

Fusing the dc ht feed to ot dramatically changes sound, why?, is fuse choking current dynamic demand (s) based on musical signal dynamics?

[pdf64]

Fusing the dc ht feed to ot dramatically changes sound, why?, is fuse choking current dynamic demand (s) based on musical signal dynamics?

That shouldn't be the case; until it blows, a fuse can generally be regarded just a piece of wire.
So something may be happening that you are not aware of, eg ultrasonic oscillation.
For someone to examine your query over the internet, it would be best for you to provide detailed photos and voltage survey.
Bear in mind that a fuse needs to cut the supply to both the plate and screen grid of the power tube.
Perhaps the best arrangement for a single additional fuse would be in the centre tap ground return of the power transformer HT winding.

If no energy is drawn out from pt secondary winding (s) the primary winding becomes a mere coil load to the utility company's feed of line power.

Think of the tungsten filament heating inside incandescent bulb fed by utility company ac feed.

So I think the weak link is the primary winding, as it appears just like said tungsten filament, only less resistive being copper filament

Why do you perceive this to be a problem? I can't see anything bad there, apart from a slight waste of energy.
The inductive reactance of the primary will prevent any significant heating / current flow.

[hewo]

New discovery:
1. Bottles pulled
2. 5y3 htr windings isolated from earth
3. Ecc83/6v6 htr windings earthed
4. This means pt defect? That 6.3 htr windings pt earthed?
5. Amp plays, but is under scrutiny because hum in background once ht applied, but how much hum is acceptable prior to abandoning defective pt? Acceptability One onehundreth of guitar signal at the spkr?

[hewo]

Whoops, pt label says 3.15green:0yellow:3.15green
And confirmed yellow earthed
So this confirms earthed 6.3 htr windings
So hum must be attributed elsewhere:
1) imbalanced leg to leg from ct of 6.3 winding
2) lack of 100 ohm resistor to earth each 6.3 htr leg
3) possible derated master electrolytic 16uf 450v
4) possible derated "hum" in 6v6 and or ecc83

[g1]

2) lack of 100 ohm resistor to earth each 6.3 htr leg

This is only done when there is no CT in the heater winding. If you want to try it, you would need to disconnect the heater CT (grn/yl).
It may help for hum doing it that way. Another way is referencing the CT to the 6V6 cathode.

[Enzo]

If you built a true 5F1, you will note one side of the 6v is grounded. To use a grounded CT, you must NOT ground either side of the 6v. If you have a grounded heater CT, then your meter will measure 3v on either end of the 6v winding, but on ohms either side will appear grounded because of the VERY low resistance of the winding.

I am aware of no example of a fuse in the B+ to the OT "dramatically" changing the sound. The fuse IS a piece of wire until it blows.

PT does not cause hum, it makes voltage. Hum comes from ripple in the supplies, poor grounding, radiated fields, etc.

You have built a single ended amp. Push pull amps naturally cancel out hum from the B+, but your single tube cannot do that. So the ripple that would sound OK in a push pull, sounds hummy in a single ended. Note your plates (OT) take B+ right off the first node. Now compare to the 5E1, note the OT takes its B+ AFTER the first node and choke, over at the second node. That design will have lower hum than yours.

You never use the 100 ohm resistors when you already have a CT grounded.

60 years ago, caps were expensive. They used 8uf and 16uf, because they were good enough for guitar amps, But today caps are cheap, so making them all 20uf or more would help.

[hewo]

Hum may have resulted from house line outlet ground fault.
Prior, wasn't as much hum, hard to distinguish the increase hum without spkr energy measurement comparison fiducial no musical demand, ht engaged.
Let me report back what's this fiducial level, no musical demand, ht engaged.
I'll accept fiducial hum if one onehundreth of musical signal strength.
Spkrs are 2x12x8ohms series = 16ohms, ot 8ohms edcor 20va.
Recall that mv a1meg is bridged to earth by 1meg metalfilm halfwatt, effectively halfing throttle fed to input grid 6v6, and there is no 224 tiedown resistor here because mv suffices as bridged to earth so appears as 504 resistor (5f1 schematic wants 224 tiedown resistor here).
Recall 6v6 gridstopper 102 resistor then feeds signal (but is not per 5f1 schematic.

[hewo]

Excellent enzo!
Will measure htdc at master electrolytic (1st node) no musical demand.
Will measure 2nd node (screen).
If amend htdc 1st node output with sb125ma fuse, I will show you folks, oscilloscope snapshots, with musical demand, the difference claimed is in fact appreciable, as during the demand transient, energy is sluggish to respond owing to the fuses behavior to pass demanded energy. A simple bypass of this amend switch will reveal the actual transient indifference.