various amp tech questions

[Leo_Gnardo]

Exactly. So now he's asking if I'll keep the amp for $100 trade in on one of mine. These trannies worth a darn?

What a wheeler dealer you are. Haven't seen any of those transformers gone up in smoke yet. I expect they're decent iron.

[Stevem]

The power trans isn't those amps do not have much in the way of peak power do the limited current output!

[Smokebreak]

What's with the 440V@65.7mA?

https://www.tubesandmore.com/products/P-TF36958

The MC equivalent doesn't list that spec.

388V FWB @ 200mA seems ok though for ~430V plates, no?

[pdf64]

The heater winding may not be much use (6.6 VAC @ 3.75 mA AC).

[Smokebreak]

The heater winding may not be much use (6.6 VAC @ 3.75 mA AC).

Yea I found that odd, too, even moreso the Fender scheme shows 3.3 per side thus 6.6. The MC is 6.3. I mean, it should be fine +-10% but I don't know why one would design it that way

[Leo_Gnardo]

The heater winding may not be much use (6.6 VAC @ 3.75 mA AC).

Yea I found that odd, too, even moreso the Fender scheme shows 3.3 per side thus 6.6. The MC is 6.3. I mean, it should be fine +-10% but I don't know why one would design it that way

I think pdf64 is pointing out the hopelessly weak 3.75 MILLIamp rating .

Somebody moved the decimal point, I suspect.

Or they wound the filament loop with guitar pickup wire.

[Smokebreak]

Doh! That mA flew right by me.

[sunnydaze]

A lot of times I see the transformer specs given in terms of VAC. Based on a lot of recent Googlin', I thought you were supposed to divide that rated VAC by the secondary voltage to get the amps rating. In this case 6.6Vac / 6.3 Volts A/C = 1.047 amps.

If that's not correct, hope someone can clear this up for me. I've been searching online for filament transformers, and most sites I'm using only provide the VAC rating. I had to google around to a lot of places to find the above explanation.

Thanks & best regards,
Mike

[sluckey]

I think you mean VA (volt/amps) rather than VAC (AC volts). VA is just another way of saying power.

[roberto]

Only if you consider the power factor as unitary, like in pure resistive loads.

[sunnydaze]

Thanks.

Slucky, your're right, I meant to say "VA" not VAC.

Here is a link to one I'm looking at - I buy a lot of stuff from RS electronics(taiwan) - they offer free shipping on everything, no matter the order size.

http://twen.rs-online.com/web/p/products/2575001/

This particular transformer is rated at 50VA 6VAC - so I'm thinking it can handle 8.3 amps.

Roberto>Not really sure whether or how to consider your comment in calculating what this transformer can handle. Taiwan's power supply is 60HZ, and I'm planning to use this to heat tube filaments (lots of tubes) - five 12a*7 types and possibly 4 6L6's.

Is the simple dividing the VA rating by the secondary voltage a safe way to calculate the capacity in way that matches the way tube filament power consumption is listed (in amps).?

Thanks for the help.

Best regards,
Mike

[xtian]

BTW, that Orange Dual Terror I repaired required two techs to do the job. The caps were glued onto the PCB, so I had my 17-year-old daughter hold the iron while I pried the caps off from the other side of the board. Teamwork!

[Smokebreak]

I've got a Deluxe Reverb RI come in now for the 3rd time in 3 weeks, with a new problem every time.

First time, owner says loss of power and no vibrato. New power tubes and putting V1 in the vibe spot fixed it. I remember thinking it was one of the better RI I've heard.

A week later, it's got a slight trailing fuzz/noise only on 2 or three notes on the neck. After ruling out external factors, I start swapping pre tubes. Strange thing is that with different guitars, it's doing it on different notes, all around E on the A string, and only with single coils. I find a good combination, we both agree it sounds good again, and out the door it goes.

It comes back yesterday, and the amp is breaking up on "3", and now generally has this awful high end breakup. Very harsh. I did more tube swapping, checked bias(22mA @420V)ran it through a working Gold, to no avail. Sounds the same on both channels.

Owner tells me it was never quite right a week after he bought it, about 4mo ago.

I'm gonna get into it today, but am looking for advice from those of you have been inside lots of these. I'm gonna start with solder joints, but I can't really find many "known issues" with these, other than sounding harsh out of the box. I would chalk it up to that, but I had it sounding good a few weeks ago.
Amp is 11 years old so I suppose I can cap it too, but that seems a little premature, though it may fall in line with the variety of problems.
Thanks!

[billyz]

I've got a Deluxe Reverb RI come in now for the 3rd time in 3 weeks, with a new problem every time.

First time, owner says loss of power and no vibrato. New power tubes and putting V1 in the vibe spot fixed it. I remember thinking it was one of the better RI I've heard.

A week later, it's got a slight trailing fuzz/noise only on 2 or three notes on the neck. After ruling out external factors, I start swapping pre tubes. Strange thing is that with different guitars, it's doing it on different notes, all around E on the A string, and only with single coils. I find a good combination, we both agree it sounds good again, and out the door it goes.

It comes back yesterday, and the amp is breaking up on "3", and now generally has this awful high end breakup. Very harsh. I did more tube swapping, checked bias(22mA @420V)ran it through a working Gold, to no avail. Sounds the same on both channels.

Owner tells me it was never quite right a week after he bought it, about 4mo ago.

I'm gonna get into it today, but am looking for advice from those of you have been inside lots of these. I'm gonna start with solder joints, but I can't really find many "known issues" with these, other than sounding harsh out of the box. I would chalk it up to that, but I had it sounding good a few weeks ago.
Amp is 11 years old so I suppose I can cap it too, but that seems a little premature, though it may fall in line with the variety of problems.
Thanks!

Check the power supply caps. I have seen more than a few of these with bad caps causing all kinds of problems.

[Colossal]

Smokebreak,

I wouldn't overlook a cap redo as part of your corrective action, especially if the amp has seen a lot of hours in its 11 years. That raises a flag.

Jesus Saves...because with the quality of today's operating systems and electrolytics, he knows better.