Egnator Rebel 30 Power Tx secondary voltages???

[robo]

Hi,i have a new build Power Tx for an Egnator rebel 30 and am not sure of the off-load secondary voltages.
Do these seem correct?

This Tx has off-load measured voltages of:

red = 340vac (HT)
white = 275vac (for Bias tap? but seems very high?)
red = 340vac (HT)
black = 0vac (GND)

green = 7vac (heaters)
grey = ct
green = 7vac (heaters)

blue = 13.5vac (LV supply)
brown = ct
blue = 13.5vac (LV supply)

I think the LV supply and heater supply is correct but am not sure of the HT and bias?
They seem too high for 2x EL84 and 2x 6v6 output tubes???

Can anyone help here or advise on the voltages in the Rebel 30?
I have a schematic but there are no voltages written in!

Thanks.

[Jazz P Bass]

For the bias winding, are you measuring Black (zero volt CT) to White?

egnater_rebel30_sch.zip

[robo]

Hi Jazz P Bass and thanks for replying.

Yes i measured the two red wires and the white with a DVM set to ac volts from the black lead.
When i initially connected the white and black wire to the pcb and turned on,the mains fuse blew,
not black and nasty,just blew.
I have connected the two red HT wires and get 475+dc volts at the standby switch
which is 25 volts over the main smoothing capacitor rated at 450v.
No output tubes in yet,and just think that the HT is too high for El84 or 6v6's??? So have not put them in and flipped standby switch on.
thanks for the schematic that is the one i have,but no voltages on it.

I am worried that if the voltages are too high i will damage something!

Any other thoughts or what voltages you think should be there,would be vry welcome.

Thanks.

[g1]

The voltages should drop to more normal levels with the tubes in. Make sure you have bias voltage at the power tube sockets first.

[robo]

Thanks for the info g1,and replying i will try it and make sure the bias voltage is there.
Thinking the bias tap was too high(275+vac),i put a 2W 22k resistor in front of the spade connector and it
has dropped the voltage by approx 60-70vac and produces -24v on the el84's,and -44 on the 6v6's as
the pots were set from before.So there is some adjustment if needed.
I will test with the provided bias test points for 40mA.

[J M Fahey]

I am worried about the 7VAC+7VAC filament winding, please recheck.
According to schematic, each "6.3VAC" labelled end goes to one 6V6/EL84 filament end.
It might be a sloppy way to name a 6.3VAC center tapped winding, but robo measured 7VAC across each half .... WTF?

Please repost voltage measured across green to green and green to grey.
Then voltage measured at the EL84 socket pins.
Thanks.

[robo]

Hi and thanks for replying J M Fahey,

Voltage measured across Green - Green = 14vac; Greens to Grey = 7vac (offload)

I put in the 6v6's and EL84's connected all secondaries EXCEPT HT,and measured
the ac fillament voltage at 6.5vac on each green connection and on each valve socket
for the 6v6,el84 and 12ax7 Phase Inverter

Strange points are these:

On the PCB written by the green wire spade connectors and on every valve base(6v6,el84,P.I)
connection it says 3.15vac!!!
Yet the schematic of PSU states clearly that the AC secondaries are 6.3vac each with a CT

Also for a second on measuring with DVM while turned and with Output valves and P.I. in, on the meter reads approx 3.15vac,then goes to 6.3vac??
Same when no valves in???

I am stumped,why does the schematic conflict wit what is written on the pcb?
Could it be wrong?

If so can i install 2x ptential dividers to half the 7vac???
Any thoughts welcome.

[Enzo]

The schematic shows the 6.3v winding by calling the ends 6.3v, and it has a center tap. If the board is labelled 3.15 at each end, it means one draftsman drew the schematic, and a different draftsman drew up the board art, and they happened to use different labelling schemes. Imagine I told you it was 6 miles to my house from yours but the map said it was 10 kilometers. Focus on what matters - you either have about 6-7v across the tube heaters or you do not.

[robo]

Hi Enzo and thanks for replying.
With all valves in but the HT not connected:

I just measured the voltage across the 3.15vac marked points on the pcb where
the green wires connect to the board,and all points on the 5 valve sockets
2x6v6,2xel84,and 1x12ax7 : MEASURES 13.44Vac and the valves are lit very brightly!

The pre-amp valves run off 12v from the other low voltage psu separately,
this is working and measures correctly.
The bias voltage is present at both pairs of output tubes


So i am thinking this heater secondary is twice what it should be???

Can i salvage this by adding potential dividers to them to halve the in-going heater vac?
If so what resistance and wattage should they be?

Any help most welcome

[Enzo]

What is your mains voltage? Any chance you are on 240v with a 120v transformer?

[robo]

Hi Enzo,

Mains voltage is 230vac in the UK,and this Tx was built for this Egnator Rebel 30 with the same primary voltages
as the original: 230:120:110
If that were so would not the other low voltage winding be twice its voltage?
Also the other windings?
I think the heater windings should have been 3.15vac each,not 6.3vac???
Is it possible to use resistors to halve the heater voltage,or even a Zener diode in the CT?

All help much appreciated

[J M Fahey]

Hi Enzo,

Mains voltage is 230vac in the UK,and this Tx was built for this Egnator Rebel 30 with the same primary voltages
as the original: 230:120:110

Ok, it was BUILT with 3 voltage options, not sure at all what YOU are using.

IF you have some 14V across power tube filament windings and to boot "they light very bright" pull them out NOW or you will burn them.

I am worried because you say "I have xx volts at some place" but Iīm never certain where the other probe is; it is NOT the same winding to winding than winding to ground.
You answered correctly

Voltage measured across Green - Green = 14vac; Greens to Grey = 7vac (offload)

but

measured the ac fillament voltage at 6.5vac on each green connection and on each valve socket
for the 6v6,el84 and 12ax7 Phase Inverter

is confusing; I see that you put the red probe on one green wire or matching pin, you donīt say where you put the black one, it may be on the other green one or on chassis/ground, not the same.

You never ever have a voltage at a certain point alone, but a voltage difference between it and somewhere else, which must be clearly defined.

If that were so would not the other low voltage winding be twice its voltage?
Also the other windings?

Transformers are .... er .... voltage "transformers" (converters) meaning they turn one voltage into another X times higher or lower , they donīt have a voltage on their own (the way batteries or generators do) so: if you apply twice the voltage to one winding, ALL others will also show twice the expected one (hint hint).
Is it damaged or working wrong?
No, itīs doing exactly whatīs expected of it.

I think the heater windings should have been 3.15vac each,not 6.3vac???

Each half should have been 3.15VAC relative to center tap or ground, 6.3V end to end ... your question omits the reference poiint so as is, is unanswerable.

Is it possible to use resistors to halve the heater voltage,or even a Zener diode in the CT?

No , the solution is to wire it properly.

[g1]

If the other windings are giving the right voltages, then the primary is probably wired correctly.
Perhaps you can use half the heater winding and make a virtual center tap.

[Enzo]

Since the transformer was "built" for this, it may not have been made correctly.

[J M Fahey]

Since the transformer was "built" for this, it may not have been made correctly.

Oh, now I see it in a very different way.
When I read:

in the UK,and this Tx was built for this Egnator Rebel 30

I understood: "why, of course, heīs telling us he bought the original one or an aftermarket version meant for that amp" (think MM / Classictone / Hammond / any commercial maker who knows Egnater well), he didnīt just pull, say, a leftover Fender amp "pull" he had lying around or some old rusty dusty transformer bought as surplus which he hopes might work.

But now I am starting to think a third possiblity which, if true, is quite mind numbing:
*maybe* this amp had a dead PT, it was burnt into a blob of charred insulated wire, molten plastic bobbin gluing everything together and even some molten blobs of copper, if a nail or crumpled aluminum paper was used as a fuse.

A replacement was ordered, winder could not count turns and measure diameter because of the catastrophic failure, so he got a paper napkin where it was scribbled:

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

* filaments: 2x 6.3 VAC, under load, which is "x" amperes <--- no big deal, amperes are easy to calculate, he wound for 2 x 7VAC no load because he knows voltage drops somewhat under load.

* other windings: no data.

- "hey, I canīt wind without data and this is not a generic transformer (say, for a Sega or PlayStation supply or anything which was ordered before), tell me what you need or what the circuit uses"

1 week later:
- " I checked some Forums, a guy who has same amp says the high voltage is 340V , another that low voltage is 13.5V , bias is 27.0V (which was read as 270V by mistake) "


Of course the winder did literally what he was asked for.

Just one explanation I can imagine, of course I am open to others.

The scenario with transformer misconnected and actually using a 117V winding on 230V mains is not absolutely impossible but unlikely because in such cases lack of needed primary impedance (half the turns means 1/4 the impedance) plus doubled core magnetic flux, well beyond saturation (unless the transformer was designed VERY conservatively , say 8000 Gauss max) normally blows the primary fuse in seconds or minutes and would have exactly doubled *all* seconday voltages.

The fact that higher seconday voltages was not proportional makes me think of poorly written/understood winding instructions.

An absolute mishmash of DC and AC volts, I have seen that before .... even here , a couple such posts not long ago.

Without going too far, Roland amplifiers specify primary voltage matching local mains, but secondary voltage is specified as what is the secondary DC voltage, and to boot, under full load, so the straight 1.41X calculation does not apply ... since drop under load must be considered ... and that from a World Class manufacturer.

Confusing Roland transformer specification on service manual and schematics: