Egnater Rebel 20 Mk I - Blown PT

[nickb]

Does anyone know what the secondary voltages for an Egnater Rebel 20 Mk I are please? If you have one and know what they are loaded and unloaded it would be massively appreciated. I don't expect Eganter will release that info.

I have one with a blown power transformer and I'm betting that it will cheaper for me to rewind than import, especially since the pound has gone to so low against the USD lately.

[Enzo]

I don't expect Eganter will release that info.

But you won't know that unless you ask him.

[olddawg]

As Enzo says. You never know until you ask.... They may have some engineering notes on their schematic and most techs are helpful IMHE. That aside. What is "blown"? If it has an open primary, it may be an open thermistor that you can find and jumper with a little surgery and take your measurements. AND... The 120v tap may be fine. If it is use a variac to make your measurements. Also... I worked on a similar Egnator last week that had a damaged voltage select switch. The way the voltage line select switch was mounted it was very easily damaged. Are you SURE the switch isn't messed up?

[Enzo]

You can usually infer voltages. 6v heaters is common. What voltage B+ filter caps? Given the tube complement and what voltage other similar powered amps use with the same power tubes, we can guess. You may find some Fender amp has a PT close enough. If it has solid state parts, then 15v supplies you can infer what AC is needed for starts. Bias winding? Easy enough to fudge.

[nickb]

But you won't know that unless you ask him.

Trust me, I asked them first.
.

[nickb]

You can usually infer voltages. 6v heaters is common. What voltage B+ filter caps? Given the tube complement and what voltage other similar powered amps use with the same power tubes, we can guess. You may find some Fender amp has a PT close enough. If it has solid state parts, then 15v supplies you can infer what AC is needed for starts. Bias winding? Easy enough to fudge.

I have done that but in this particular case there is little room for error. The HT and AC heaters is easy enough but the bias and LV supply is tricky. Get the bias too high and I'll have to change the bias resistors and these are buried on one of the PCB. Also there are two sets of them as there are 6V6 and EL84 output tubes. Too low doesn't bear thinking about. Same with the LV winding, too low and it won't regulate, too high and the heater regulator will cook. Yes, I can do it, but it's all time and that is multiplied by the fact there are no component values on the schematic.

[nickb]

As Enzo says. You never know until you ask.... They may have some engineering notes on their schematic and most techs are helpful IMHE. That aside. What is "blown"? If it has an open primary, it may be an open thermistor that you can find and jumper with a little surgery and take your measurements. AND... The 120v tap may be fine. If it is use a variac to make your measurements. Also... I worked on a similar Egnator last week that had a damaged voltage select switch. The way the voltage line select switch was mounted it was very easily damaged. Are you SURE the switch isn't messed up?

It's virtually a dead short. With all the secondaries open and my variac set to 10V it's puling 50W from the socket. Thx for the voltage selector switch idea. That one didn't cross my mind. It is recessed behind a transparent panel and it doesn't appear to be out of position but, yes, I'll check. I'l also try the 120V and 100V taps.

Update: The switch is OK and no better on different taps. Bother.

[nosaj]

I have done that but in this particular case there is little room for error. The HT and AC heaters is easy enough but the bias and LV supply is tricky. Get the bias too high and I'll have to change the bias resistors and these are buried on one of the PCB. Also there are two sets of them as there are 6V6 and EL84 output tubes. Too low doesn't bear thinking about. Same with the LV winding, too low and it won't regulate, too high and the heater regulator will cook. Yes, I can do it, but it's all time and that is multiplied by the fact there are no component values on the schematic.

Will this link help you figure out what you need? Calling them may help they love to talk.
Mercury Magnetics - Egnater amp transformers

nosaj

[J M Fahey]

Please post the schematic you have, even without parts values.
Again, even if itīs some kind of simulclass with mixed tubes output , you have 2 ways to solve that:

1) get a small winder, ideally a guy working on his own, who will have the time and oatience to unwind it and count turns, wire diameter is a given,of course.
That said, you will end up with a fresh transformer as underdesigned as the original one, which wonīt last much longer.
At least, thatīs what rewinders around here do, with absolutely no data or information, so only option is to clone faithfully

2) I would use the next larger core size , check available space, and next higher wire diameter.
That implies redesigning, of course, but as said above:

* heaters are known

* +V can be copied from similar amps, tubes are not exactly breaking news novelties, and +/- 10% error wonīt even be noticeable.
In fact Iīd rather err 10% low, guitar tubes by definition are already abused, we do not need to further that.

* slight problem might be bias, as you mention, but itīs usually adjustable , unless he also copied Mesa on that ... but letīs wait for the schematic, in general again go for whatīs usual for those power tubes.

Worst case you can specify slightly higher AC bias voltage tap and trim it down as needed with a couple resistors, current there is very low anyway.

* as of +/- 15V supplies, aim for +/- 20/22V raw and you wonīt be far from it.

Think like any regular designer would do, I bet the original one knew his job, just was asked/pushed to make it *CHEAP*

It could be much worse, it might have been a Zinky design

So we wait for your Schematic

[nickb]

Will this link help you figure out what you need? Calling them may help they love to talk.
Mercury Magnetics - Egnater amp transformers

nosaj

Thx I had seen that but there is no data. Grr.. Still, I love the the bit about "they love to talk". That's not underhanded is it? It might be perfect for my Rebel clone project... I will give it a try. Nothing ventured...

Did some readings with it on it's own on the bench. There is no doubt that the HV secondary is the one with the short. I would say the LV winding is 14V. This ties in with a handy silkscreen of 17VDC for the unregulated side of the LV supply.I'm estimating the HV at 265V based on Internet comments of 367V for the HT.

Talk about a quart squeezed into into a pint pot! This thing uses every square inch of volume and has 3 stacked PCBs. Two 6V6's, 2 EL84's and four 12AX7s all on a tiny chassis that is smaller than a Champ. Bleugh!

Using a flashlight I was able to see enough of the lowest PCB where the bias components are that should allow me to make a good guess at the bias tap voltage. If I get that too high it's easy enough to drop.

[nickb]

Please post the schematic you have, even without parts values.
Again, even if itīs some kind of simulclass with mixed tubes output , you have 2 ways to solve that:
1) get a small winder, ideally a guy working on his own, who will have the time and oatience to unwind it and count turns, wire diameter is a given,of course.
That said, you will end up with a fresh transformer as underdesigned as the original one, which wonīt last much longer.
At least, thatīs what rewinders around here do, with absolutely no data or information, so only option is to clone faithfully
2) I would use the next larger core size , check available space, and next higher wire diameter.
That implies redesigning, of course, but as said above:
* heaters are known
* +V can be copied from similar amps, tubes are not exactly breaking news novelties, and +/- 10% error wonīt even be noticeable.
In fact Iīd rather err 10% low, guitar tubes by definition are already abused, we do ot need to further that.
* slight problem might be bias, as you mention, but itīs usually adjustable , unless he also copied Mesa on that ... but letīs wait for the schematic, in general again go for whatīs usual for those power tubes.
Worst case you can specify slightly higher AC bias voltage tap and trim it down as needed with a couple resistors, current there is very low anyway.
* as of +/- 15V supplies, aim for +/- 20/22V raw and you wonīt be far from it.
Think like any regular designer would do, I bet the original one knew his job, just was asked/pushed to make it ****CHEAP****
It could be much worse, it might have been a Zinky design

So we wait for your Schematic

Here you go Sir JMF. Your schematic awaits you...


Edit: AW, don't bother looking. nosaj's below is MUCH better...

[nosaj]

Here you go Sir JMF. Your schematic awaits you...

Here is one that has voltage values for caps which may help with inferring your need values easier
nosajREBEL20sch 8-09 with Values.pdf

[nickb]

Here is one that has voltage values for caps which may help with inferring your need values easier
nosaj[ATTACH]39827[/ATTACH]

It's got component values too. Woo Hoo! Well done Mr Nosaj I'm pretty much home and dry now...

[nosaj]

It's got component values too. Woo Hoo! Well done Mr Nosaj I'm pretty much home and dry now...

I got it from another thread here somewhere and d/l'ed and lost track of the thread.

nosaj

[nosaj]

Thx I had seen that but there is no data. Grr.. Still, I love the the bit about "they love to talk". That's not underhanded is it? It might be perfect for my Rebel clone project... I will give it a try. Nothing ventured...

Did some readings with it on it's own on the bench. There is no doubt that the HV secondary is the one with the short. I would say the LV winding is 14V. This ties in with a handy silkscreen of 17VDC for the unregulated side of the LV supply.I'm estimating the HV at 265V based on Internet comments of 367V for the HT.

Talk about a quart squeezed into into a pint pot! This thing uses every square inch of volume and has 3 stacked PCBs. Two 6V6's, 2 EL84's and four 12AX7s all on a tiny chassis that is smaller than a Champ. Bleugh!

Using a flashlight I was able to see enough of the lowest PCB where the bias components are that should allow me to make a good guess at the bias tap voltage. If I get that too high it's easy enough to drop.

No not underhanded by me. But when I left a message one time, it was the president of the company that called me back we must have talked for like an hour. Very nice and helpful guy eho helped me out even though I didn;t buy his product.

nosaj