Egnator Rebel 30 Power Tx secondary voltages???

[Dave H]

* Primary: 0/100/117/230V . <-- so far so good, it matches his daily experience, he got it right.

If it's wound for 230V then the secondary voltages will read high in the UK. 230V is the 'harmonized' EU voltage. The voltage in the UK is supposed to be 240V but measures nearly 250V where I live. The voltage in France is still 220V. The 230V EU standard is a fudge because countries didn't change over to 230V as both 220V and 240V fall within the EU standard of 230V +/-10% so that's OK then?

[robo]

Hi, J M Fahey,

Thanks for your insights into this problem.

To answer your questions:

1): Yes this Rebel 30 had a shorted power Transformer.
All secondaries gave a measurement but the Primary was shorted so dead.

It was dead but NOT burned-there was very little smell even close up to it when off the amp.

I sent it to a Transformer winding company here in the UK along with a detailed description
of the required secondaries taken from the available schematic and them determining the
HT when taking the dead Tx apart.
Maybe the winder could not count the turns or maybe they used the schematic value for the filament?
I dont know.
I believe the schematic filament voltage is mislabeled and wrong as the pcb has very clearly
written 3.15vac at the spade terminals where the two green filament wires from the Tx connect,
and on each valve socket where they are wired across to from the spade terminals.

The other LT winding was to provide 12vdc for the 4 pre-amp valves,and +/- 12vdc for the opamps and relays.
This was clear on the schematic and i detailed this in an enclosed sheet with the schematic and original Tx.

They determined the final HT voltages,i suggested they would possibly be around 300vac and bias 100vac!

(From your previous reply):
2): When measuring voltages i had the Black lead on the CT(or gnd where it connected on the pcb),
and measured each green wire of the filament winding:

Offload = 7vac

then as you asked across the two green wires

Offload = 14vac

Then with the tubes in,Loaded:

Black lead to grey/Gnd,and Red to each green wire

= 6.5vac

and across the two greens(Black to one green,Red to the other green)

= 13.44vac

3):
Yes i mean 3.15vac relative to filament CT/Gnd.

Apologies if i was vague and confusing i just want to get this amp up and running
rather than trash it!

Thanks

[robo]

Hi g1,

Thanks for your help.
When you say virtual CT,How would this be achieved and what components would i need to do it?

If you are using one leg, i.e 1 x 6.3vac would you have to connect the two legs together to achieve full current from the winding?

Hoe would i set up a virtual CT?

Thanks

[Dave H]

When you say virtual CT,How would this be achieved and what components would i need to do it?

If you are using one leg, i.e 1 x 6.3vac would you have to connect the two legs together to achieve full current from the winding?

Hoe would i set up a virtual CT?

2 x 100ohm resistors

Don't connect the two legs together. They are out of phase!

Connect the two 100ohm resistors in series between one 6.3V leg and the CT. Ground the junction of the two resistors. Connect the heaters to the same 6.3V leg and CT

Edit: Don't ground the CT (as the schematic does) The junction of the resistors should be the only ground point of the heater circuit.

[robo]

Hi Dave H,

thanks for replying,i am at my wits end trying to salvage this Tx and therefore the amp.

I get your instructions,is this not a potential divider?
and if i can do it on one leg,why not the other giving me 2 x 3.15vac
which is what seems to be needed according to what is written on the pcb?

One more point will the 100ohm resistors get particularly HOT?

I have 4 x 7W 100 ohm green vitreous resistors
I could mount them in the air directly onto the spade terminals
and ground the two ends to the ct spade connector also?
Will they restrict current from the windings to the heaters or
if so is it minimal?
This winding must be at least 3AMPS for the output tubes and P.I.

Thanks for suggesting some kind of solution.

[robo]

Hi Dave H,

I think i misunderstood your instructions for a virtual earth.
Is this correct:
This is what you would do when the power tx only has one winding and no ct,
which is the same as has been done on many old Fender amps with the 2x 100ohm
resistors grounded at the pilot light fed by the filament winding to work?

Ok i understand that now my remaining question is would only half the current
be available through just one of the windings on this Tx,or full current through just this one winding?

Thanks again for your help.

[Dave H]

...and if i can do it on one leg,why not the other giving me 2 x 3.15vac
which is what seems to be needed according to what is written on the pcb?

One more point will the 100ohm resistors get particularly HOT?

You can't use the other leg unless the heaters are split into two groups and the CT grounded. It should be as the schematic below.

The resistors don't carry the heater current.They only have 3.15V across them, power is therefore 3.15^2/100 = 100mW. 0.5W resistors would be OK.

[Dave H]

now my remaining question is would only half the current
be available through just one of the windings on this Tx,or full current through just this one winding?

Hard to say as we don't know the current rating of the winding but I think it should be OK for the full current through one winding as it only drops to 13.44V when powering the heaters with double their rated voltage! They must be shining like light bulbs if they are not already dead.

[robo]

Hi Dave H,

Seems like this will work,i will try it out.
Yes the valves did light up like Xmass,but i turned them off PDQ.
Hopefully they are not damaged,i will see soon.

Thanks for all your help and suggestions.

[J M Fahey]

Starting from the end:

Apologies if i was vague and confusing i just want to get this amp up and running
rather than trash it!

Oh, don´t worry about that; in fact what IS annoying and confusing is that Egnater themselves are so.
The no values schematic is a mess, the filament windings are wrongly labelled, period, specially since the PCB values are correctly printed.
People who routinely deal with tube amps won´t have problems, because they "already know" but others, even if Pros in their respective areas , will just do what is asked for, literally.
Why/how would a regular transformer winder know that tubes we use run on 6.3V end to end?
Unless they are Drake or Dagnall or Partridge, the classic UK transformer powerhouses which have been supplying guitar amp makers since forever, and even so ........
We see tubes everywhere but truth is that when I started studying Engineering in 1969 , they were no longer taught at the University, period.
Do the Math

1): Yes this Rebel 30 had a shorted power Transformer.
All secondaries gave a measurement but the Primary was shorted so dead.

It was dead but NOT burned-there was very little smell even close up to it when off the amp.

I sent it to a Transformer winding company here in the UK along with a detailed description
of the required secondaries taken from the available schematic and them determining the
HT when taking the dead Tx apart.

I shudder at being so accurate sometimes, specially if I don´t likewhat I see.
To say it bluntly, I´m not sure that transformer will do.
2 problems:
* transformers are very limited in window size, which determines how much copper you can fit in there, so if you wind for higher voltage (what happened here), you use thinner wire or all those extra turns won´t fit, there´s no space available.
To boot, even the original transformer was too tightly specified (to say it kindly) .
Do you keep a copy of the specs you sent the winders?
It might help us guess what they did and maybe salvage it.

But I´m not too optimist about that; I guess the only true and safe solution to repair your Rebel 30 will be to:
a) accurately determine exact voltages needed
b) order a new one
Sorry.

Maybe the winder could not count the turns or maybe they used the schematic value for the filament?
I dont know.

I guess he did NOT count turns but used a mix of the few visible values and some supplied by you, clearly there was a communications problem.

I believe the schematic filament voltage is mislabeled and wrong as the pcb has very clearly
written 3.15vac at the spade terminals where the two green filament wires from the Tx connect,
and on each valve socket where they are wired across to from the spade terminals.

I bet they never saw the PCB but at best the (poorly labelled) schematic.

The other LT winding was to provide 12vdc for the 4 pre-amp valves,and +/- 12vdc for the opamps and relays.
This was clear on the schematic and i detailed this in an enclosed sheet with the schematic and original Tx.

Can you please post a copy of that enclosed sheet?
maybe you have the .txt or .doc saved in your computer.

They determined the final HT voltages,i suggested they would possibly be around 300vac and bias 100vac!

Well, they were way off the mark, but considering they were shooting in the dark, can´t be blamed.
Question to fellow members: what would a typical/average/usual +V voltage be found in a 30W amp using these tubes?
That multiplied by .707 will give the AC voltage on each HV winding side.
340VAC is reasonable fo a 6L6/EL34 powered 50/60/100W amp, meaning a hot around 480V +V ; probably deadly for EL84, although 6V6 can take that.

And 270VAC for bias means there was a HUGE misunderstanding.

I suggest we collectively "redesign" your transformer as to what is really needed in your amp, including proper bias voltage, and then you order a new one

At leastyour Rebel 30 will work properly, I fear tryingbto salvagebthe one you have will damage both amp and transformer.

Only IF you had wound it yourself (or a friend) I would have suggested to pull secondaries, keep primaries since they are presumed well made and rewind as needed, but sadly that´s not the case.

Just curious, how much did you pay for it?

If too much, *maybe* one of the excellent Polish winders can offer you something for a good price; an USA made one will pay lots of freight and possibly some Customs Tax

[Dave H]

Question to fellow members: what would a typical/average/usual +V voltage be found in a 30W amp using these tubes?
That multiplied by .707 will give the AC voltage on each HV winding side.
340VAC is reasonable fo a 6L6/EL34 powered 50/60/100W amp, meaning a hot around 480V +V ; probably deadly for EL84, although 6V6 can take that.

My 4 x 6V6 (cathode biased) amp just about makes 30W with a B+ of 375V. Transformer AC voltage is 280V bridge rectified so I don't think it needs to be 340V AC.

[g1]

One more suggestion. If all other voltages are in the ballpark (bias winding can be dealt with as separate issue) and it turns out the heater current demand is too much for the 1/2 winding, a separate transformer could be used for the heaters only.
I agree with Dave H that it seems the 1/2 heater winding should be ok, but if the 6.3V drops too much or the transformer overheats, the a separate heater transformer could be used.

[robo]

Hi J M Fahey,

Apologies generally for gap of last few days,a couple of other emergencies occured i had to attend to.

I dont have a copy of the enclosed sheet as i wrote it by hand.In retrospect i should have made a copy,
i will in future.
I am very dissapointed with Egnator,i have e-mailed them many times and have received nothing back.
I cant believe the zero customer service they seem to have.Reminds me of another boutique-ish amplifier manufacturer
with the initials B C whom was equally non responsive,but at least i did eventually get a reply.

I have decided to install a 39v 50W Zener Diode in the HT secondary CT to bring down the HT.
The bias is already too high and i have installed a 2W 22k resistor in series to the connector on the pcb
to drop some voltage.....that seems to work fine.
Used one half of the Heater winding and installed the virtual earth...that is providing the correct 3.15 vac to the
pcb.

The Zener Diode dropper on the CT of the HT winding seems to be a well used and effective solution to dropping some HT
voltage,but it gets hot,but can be mounted on the metal chassis.
What do you think? Should i go for a new Tx?

Thanks for your help.

[robo]

Hi g1

Have tried the virtual earth and it works but am in the process of dropping the HT with a 39v 50W Zener Diode in the CT
I will monitor the voltages and temperature of the Tx while testing.
If i need to i could use a separate filament Tx as you suggested.

Thanks for your help

[52 Bill]

Is there some reason that you can't go back to the winder and have the windings redone the right way?

Adding an additional transformer and a Zener network seems to be a lot of work to make something functional and still not really right.