Echolette mic transformer

[Goodizzy]

I was browsing this forum yesterday and noticed someone had posted a question regarding the Echolette M40.  I have one collecting dust in the music room, having recapped and used it a few years ago.  It is a bit of a junker, missing most of its case and with a bent transformer bolt that has warped the chassis a bit.  I have already fabricated/punched a rack plate to mount it to.

Since I won't be able to resell it and I do enjoy the sound, I'd like to experiment a bit with it.

My idea is to add a mic transformer to two or the four inputs and use this as a live mixer/vocal PA for the music room it currently occupies.  As I only plan to use it for vocals, are my options for transformer opened up a bit?  (I.e. Can I get away with using an Edcor or cheaper/octal/vintage tube PA).  I would still like to have pretty decent quality, and if I have to swing for two expensive ones, that is not an issue.  Especially if the distortion would be affected by gain/volume.

Would anything in the 1:7 to 1:10 range work?  Most of the mics here are 150/200R, with the SM57/58s he higher impedance at around 500R. 

Additionally, as the four inputs are each 1/2 of the 12AX7, is there any benefit to splitting the mic transformers between V1/V2?  (I.e. Not having both transformer inputs on a single valve)

Would it be worthwile to ditch the 2xEZ81 in favor of silicon diode FW bridge?  To increase filter capacitancr and stiffen the power supply?  (Or would the sag when this thing is cranked be pleasing I wonder)

I'd appreciate any input.  I hope everyone is having a pleasant New Year!

 

[Whoops]

Would it be worthwile to ditch the 2xEZ81 in favor of silicon diode FW bridge?  To increase filter capacitancr and stiffen the power supply?  (Or would the sag when this thing is cranked be pleasing I wonder)

Hi, I guess for vocals not having sag would be better. For that job having a solid state rectifier would be preferable.

I really think you could give it better use if you use it as a guitar amp, it sounds really nice on a guitar.
I guess for vocals, with the limitations it has you would not use it's potential like with a guitar and just have a weak PA system.

 

[Goodizzy]

I am willing to rework the power supply to accomplish that. 

I am unsure why this particular amp would be bad for vocals?  It was used semi-professionally during the 50s and 60s in clubs as a PA.  The OT and PT are quite beefy and the output is 32W UL. 

The information I have from some German sites indicates a frequency response of 40 Hz-15KHz +- 1dB.  While not "hi-fi", that doesn't seem bad for vocals?  Live vocals, at that?

Maybe I am missing something-  I am not disputing your conclusion, only wondering what makes this particular circuit not worthwhile?

I had intended to leave two inputs open for guitar, etc.

 

[Whoops]

The demands of the 50s and 60s are not the same people have in 2017.
Hey, in the 60's mucisians were using the 4 inputs on a Twin Reverb to amplify all the band, everything was connected there.
There's so many reasons I could give to you, but just think about the development of drums and how loud drums were played in the 50's compared to nowadays.

Even in cheapest range of vocal PA's you have today it would be hard to find one with such Low Power.

but the biggest reason is this:

https://www.youtube.com/watch?v=4kD9_W9oZtc

Of course it's you amp and you will give it the use you want, and I wish you all the best in achieving your goals.

Just my 2 cents!

 

[Goodizzy]

That makes sense I suppose, though it seems like it could get loud enough for smaller-medium rooms.  Oh wel,, that video is quite the sell!

I wonder if the larger 100W/120W PAs could be viable?

 

[Whoops]

I wonder if the larger 100W/120W PAs could be viable?

It really depends on your uses and your needs.

I'm a studio and live sound engineer, I work with a band where the singer uses 3x Martin Audio LE1500, when the vocal is already on the verge of feedback (and after EQuing the first feedbacks) he still asks for more voice on the monitors, so I really can't tell nowadays. Of course none of the other musicians ask for his vocals on their own monitors.

By the way the Martin LE1500's ask for an amplifier of 800-1500W into 4 ohms each, and it seems not enough for his particular needs.

 

[Goodizzy]

That's interesting.  I appreciate your time, I don't think I had given it quite as much thought.  I suppose there is a reason no one is doing it AT ALL! 

The language barrier doesn't help either.  I just translated THD (Klirrfaktor) and saw that it is listed as >2% at 1KHz on the M40 spec.  That is certainly not hifi...

I'm guessing that implies the OT isn't good to repurpose for anything other than an instrument amp?  I guess it will have to lie as is!  It is a nice guitar amp

 

[PRR]

> add a mic transformer to two or the four inputs and use this as a live mixer/vocal PA

A SM58 through a 1/4" adapter (no transformer) and a rock-voice should drive that thing to full 30W output.

Try that before you spend money.

 

[Goodizzy]

That makes enough sense.  Now I have to put it back together!

The Germans certainly were efficient in cramming a lot of valves in not a lot of space.  The PT is sitting right behind the preamp stages.  It's amazing how hum-free these can be though.  My original reason for pulling it out was to see if moving the PT would make a difference.  It has to go on a rack plate regardless.

Many thanks all

 

[shot]

Don't underestimate M40!
After recording on a lot of guitar amps through the years, I got a chance to record M40 paired with 2x10" Echollete cabinet.
This amp can deliver unbelievable guitar sounds!
We tried it with few different cabinets and it was okay. But only when they got original Echollete cabinet this thing blossomed!
Even though M40 is meant to be used on bass guitar, it excels on electric guitars!
I'd pair it with a good cabinet and keep it in a studio!



Luka

 

[Goodizzy]

I wasn't aware it was intended to be used with bass guitar?  How so?

 

[jensenmann]

IIRC the Echolette B40N was intended to be their bass model. I used to play one for these for some time. It´s a fantastic recording amp. Not very loud, but sonically close to a Bassman.

 

[panman]

I believe there`s some confusion here. As mentioned, B40N  was meant for bass, but also BS40, but not M40.
They are all terrific guitaramps, when enough work has been done to get them to specs. You need to swap all the capasitors in general including the filter caps. You can improve the sound of M40 by eliminating the ultralinear connections and rewiring normal.

 

[shot]

Even though M40 is meant to be used on bass guitar, it excels on electric guitars!

Oh, it was my mistake! Yes you are all right - M40 is not for bass. I've mistaken it for B40N that my bass player owns.
It was my morning coffee post so I messed up!
But I still stand to the fact that M40 is fantastic guitar amp!
I prefer it more than B40N

(btw, it's funny when I went to qoute myself! Never did that! hehe!)

 

[abbey road d enfer]

The language barrier doesn't help either.  I just translated THD (Klirrfaktor) and saw that it is listed as >2% at 1KHz on the M40 spec.  That is certainly not hifi...

You would be surprised at the distortion figures of period HiFi valve amps...

 

[abbey road d enfer]

My idea is to add a mic transformer to two or the four inputs and use this as a live mixer/vocal PA for the music room it currently occupies. 

This model was primarily intended for vocals. Which did not prevent owners to use them with guitar, bass or organ...
The Beatles used extensively Echolette PA's during their German tours, although larger ones that this 30-watter, which unfortunately did not prevent the groupies screams to cover them.

As I only plan to use it for vocals, are my options for transformer opened up a bit?

I would suggest you try one of these in-line transformers, one orifice female XLR, the other male 1/4".
https://www.bhphotovideo.com/c/product/431406-REG/Hosa_Technology_MIT_435_MIT_435_Female_XLR.html

Would it be worthwile to ditch the 2xEZ81 in favor of silicon diode FW bridge?  To increase filter capacitancr and stiffen the power supply?  (Or would the sag when this thing is cranked be pleasing I wonder)

Sag is not a desirable feature for vocals. Beware that going SS will increase the B+. You may need to slow-start the capacitors, and you will need to readjust the output tube bias (which fortunately are separately adjustable).
The voltage selector seems to have a 250V position. I would suggest you use it.

 

[Goodizzy]

That clears things up regarding the bass amp!

For what its worth, I have recapped and had this amp going a few years ago.  At the time I had only run guitar through it.  I am more interested in its potential as a vocal amp, however.

I think I will reassemble and run a few mics through.  I know it won't get ear-shakingly loud, but its use is limited to personal.  I have been keeping my eye out for the bigger brothers, te 100W/150W valve mixers/power amps.  That is next on my list as well as the Altec 1569 80W, which I hear (several) powered Shea/Candlestick for the Beatles!!!

Does anyone have a voltage charts for this amp?  I know from reading on the internet that the PPP EL84s are run past spec, meaning they must have over 300V on the plate?  My previous measurements when this was running concurred. 

Edit:  I forgot to add that the voltage selector was broken when I got this so I have "hard-wired" it to 130V based on diagram.

Also, the spec sheet, in german-
http://www.el-me-se.de/old/pdf_files/M40.pdf

 

[abbey road d enfer]

Does anyone have a voltage charts for this amp?  I know from reading on the internet that the PPP EL84s are run past spec, meaning they must have over 300V on the plate?  My previous measurements when this was running concurred. 

Looking at the schemo, I would think the B+ voltage without signal is close to 350V, but with the sag due to the transformer and the EZ81's, I would think it decreases to about 300V at full blast, which would be in accordance with the datasheet that indicates 17W (from a single PP) with 300V B+.
The Fender Blues Jr. runs them at 330 V, which would probably be what you would get with SS rectifier and the selector on 130.

 

[Goodizzy]

Thanks.

I guess that gives me 30V to drop with SS rectifier.  I could increase cap value though with the SS rectifier.  I will have to do the math and use PSUD.  Either way, since it is going on a rack, in a box, I will seperate the PSU and have the rectifier switched between valve and SS. 

Would a thermistor slow start the caps?

If this is too basic and you can point me to link/reading that will work just as well.  I'll take a look at the Blues Jr schematic.

 

[abbey road d enfer]

Would a thermistor slow start the caps?

Yes, but not enough for an awakening from a long sleep that needs a Variac or a 60W bulb (incandescent or halogen, not eco nor LED) in series with the mains. But I would recommend you use a thermistor on the PT primary.