The french

[Racing]

So what have i gone n done now? Weeeeell...i picked this up for SnG on German e-bay basically having no idea what so ever what it is.
Took delivery of it today and STILL DON`T!
Seing a few pointers it MIGHT be french of origins tho.



Concluded from the pics was a couple of things. First up it carries a mic transformer on the one short side and this is clearly marked "Melodium Paris". That atop this thing sport (-ed) octal tubes only. That..points us in the general direction of Italy,France and in turn Scandinavia at the time. Which i guess to be late -40´s or thereabouts.
The "coke bottle" shaped powertubes was a give away too i´d say. Either really early 6V6´s or 6L6´s in my book.



That said there´s a few design decisions that i question. See them two tubes lower right? They´re BOTH 5Y3GT´s and in para.
Huh?
Yes. Designer optioned to run twin rectifier tubes in para. However..that kind of becomes a bit up the proverbial wall IMO as...twin 5Y3´s from a perspective of mA capacity AND heater current comes to about...one 5U4. WTF?
Weird to say the least.
When i first saw the pics only i thought to myself that they were different rectifier tubes,for whatever reason,but..nooooo...



Right? So powertransformer to the left and output transformer to the right then?
Wrong.
Powertransformer to the left alright but the other piece of iron there is a choke of some sorts. Haven´t gotten around to check how it´s hooked up but seing the size of it i´d wager to bet it´s one of them jobbies that were all the rage at the time being installed between PT´s centertap and ground. Wouldn´t surprise me one yota.
OT in turn is to be found within the chassis.

So what about that metal box then? At first i thought it was a "shelter" for old style electrolyte capacitors but..i was wrong.
Within resides the actual preamp tubes. As you can see there´s a small noval tube in the background. An old Telefunken ECC-83.
But? I told that the amp was based on octals? Yep. Amp has been modded to take novals somewhere down the line. That "preamp box" holds yet another 83 and in turn an EF-86. Cool!



Right. Capacitors. Siemens capacitors actually. Might be that these were installed as the amp was converted for novals? Beats me but...whatever really.
Why the swap? Your guess is as good as mine.



Microphone transformer. As you can see yourself..."Paris".
Right next to it "regular" inputs in turn. Yes,this used to be a PA amp.



As you can see 5Y3´s from different eras. Hm. Sry to say they were so loose in their sockets so the older one of them had worked itself free and....
Well. Got quite a stash of 5Y3´s truth be told but...see no reason what so ever not to swap for a 5U4 instead and..got quite a few of those around too. (Or a 5V4 for that matter)
No matter,sockets are garbage that´s for sure.



Electrical safety was sure regarded different back in the day. Yep. That to the right there is the main voltage selector and yep..the actual selector piece carries a "fuse" within. In reality a piece of copper wire "rated" at 2A. Mains fuse installed... . Selector spans from 110VAC to 240VAC so..set to go.

The other panel in turn is for speaker out and indeed this piece carries output impedances we use to this day.



Innards. Yep. That there is the output transformer. Gonna try and examine the piece more indepth for more clues of origins but..i don´t keep high hopes on that one.

That said.
What to do with it? As is this is a ultralinear hooked twin 6L6G amp in cathode bias. So a decent power estimate stock i´d wager was around the 25-30 watt mark or so.
Of course that´ll all change as it´ll become a fixed bias amp with the odd bits and ends tossed at it.

Chassis tho. I dunno. I don´t mind it being ugly,on the opposite-him with the ugliest amp onstage that rocks the hardest wins all the marbles. What i DO mind is the actual layout of it and the imperative part here is functionality as a guitar amp. That and way more important than anything else,electrical safety.
Ergo i´m giving a fresh chassis some thought. They´re cheap enough after all and the goodies of the amp,the transformers..choke and powertubes are there no matter which chassis.

Well.
To be continued lads.

[mackerelmint]

When I first looked, I thought of an old friend of mine who used to work on cars and complain that french cars had the engines in upside down and backward. So with that in mind, I wondered if it had some bizarre and inscrutable circuitry decisions made... sure enough, eh?

[Racing]

Tell me about it!!



Sry about the real poor quality pic,dunno what happend.
Todays update none the less is that this thing at least works. Yep. Gave the vitals a go over. Mains breaker was gummed up beyond anything i have ever seen at least,but a little jogging and some elbow grease made it perform to former glory.
Jumpered an IEC jack in there,coupled with a safety ground wire (which it doesn´t sport stock).

Both of the 6L6G powertubes checked out. Rather spaced apart as far as running values,which brings that they weren´t exactly matched but ya can´t win ´em all i guess. Then,no matter really as i´m going to convert the piece to fixed bias anyways and as i do bias will be individual trim,as per normal when it comes to my amps. In other words no harm no foul.

Yep. The thing works alright. In 220VAC mode we´re seing like 340VAC from each tap vs ground. However,in 220 mode heater voltage is up as well.
In 240VAC mode the thing hands me a mere 315VAC and that will make the thing come up short as far as B+ IMO...so question is if it won´t be worth the effort to install highpower series resistors for the all in all 3 heater windings. Yep. 2 of them are regular 6,3V one and then there´s the 5V one for the tube rectifier.
Main reason for this my reasoning is that by now i´m rather familiar with how the old 6L6G tubes react as far as voltage and although them 315 under load will hand me somewhere short of the 400VDC mark...nah. I want more. Ergo,220VAC mode it is.

So. Amp works. It is an ultralinear jobbie. Ie;the wiring for the screens of the powertubes are routed via a winding on the output transformer.
Many seem to believe that UL HAS to be "taps" off of the main OT winding,but this is false as the UL principle is mainly one of AC. Ie;signal in this case.
Screen resistors? Yes. 1K worth for each of the 6L6´s.

That massive choke in turn. Well. Here´s another telltale as far as the amps age cause the choke is set to be the first hit out of the tube rectifier(-s). Now... Someone´s poked around alright because we see that choke AND a first hit of an e-lyte. This DOES increase B+ voltage by a fair margin but normally simply isn´t done. It is EITHER a choke filter or a capacitor. Not both.
Anyways. Choke is of a massive 50H which figures seing how it´s setup. For those of ya that normally don´t fool around with chokes a regular choke,doing its job BETWEEN first hit and g2,is normally of 3-6 Henry. In other words that massive stock choke is either installed per stock (first hit) OR between the powertransformer HT centertap and chassis ground.
In this case..none of the above.
See no reason what so ever to put that to use seing the options available to us today. A choke might be,but in that case per normal,since like the -60´s,which means between plate voltage for the output transformer and the taps for the screens/g2.
The UL in turn i´ll just scrap.

Well. Appreciate that it´s hard to see but i jumpered a pair of regular telejacks in there and gave it a go. Nothing to write home about,that much is for sure. For the better i guess.

After having spent some time with the unit today it strikes me that this amp has undergone severe work at one time. VERY much of the capacitors and what not within has been replaced,and basically all of them with Siemens manufactured pieces.
Those that have NOT on the other hand...carries lettering in French. Hm. Starting to sway away a bit from France as country of origin and more leaning towards BeNeLux at the moment. French AND German components and in turn a powertransformer that´s rather similar in looks to what we see in old Rodec amps from Belgium. Hm.

As i tried the amp out i just shoved a 5U4 in there. As i build the amp up again that´ll be replaced with a 5Z3. Same tube from a performance POW,just uses a different socket. That and that i got craploads of them around.

Rumbling around the unit today i came to the decision that this thing needs a chassis swap. Looks of it be damned,it just IS NOT safe and can not be made so in a simple manner.
Ergo i´m going to reinstall the transformers and what not into a smallbox Marshall chassis. Ie; a JTM-45 one.

[wproffitt]

Racing,
As someone who is currently building his first amp using a turret board and some old wiring diagrams, the inside of that chassis looks like a the analog electronics equivalent of a scene from one of the Hellraiser movies to me! A chassis transplant seems like a good idea. I just found out that my wife's uncle works on old pre-war radios as a hobby. I'm sure he's seen some wild things inside of those too!

[Racing]

Cool!

Yeah. How we regard electrical safety especially has come a long way since this thing was first up put together and secondly when it saw the conversion. My main,and only really,reason for the chassis swap is...that.
How the voltage selector is exposed for instance. That simply isn´t an option today. I´ll keep it but recess it in a rather profound manner. In turn chassis is made from what seems 2.5mm (0,1") thick steel. Madness. That thing´ll take a nuclear blast.

That the way it´s built might strike the common guitarist as a maze...i appreciate that. This way of doing it however is TRUE so called point to point. One component leg to the next. Using for instance turret or tagboards in reality is not.

Tag and/or turretboards tho ARE a giant leap forward from many an aspect. Electronics enjoy law n order. Always have,always will. To the point when we today design PCB´s for tubeamp work we HAVE TO take this into account. Creepage and what not is commonplace. Just take the cheaper Blackstar amps with their "controlled" bias setup. Folly,just pure folly,and the main reason-IMO-why the Blackstar studio and stage series can be picked up for a song. There´s more examples of poor PCB design out there tho,take my word for it. Even Fender has fucked up...as has Engl and a bunch of others.

Using a turretboard for basis in a build tho IS slow. No argument,but when talking low volume i for one think it is THE way to fly. Main reasons for that is that first up it´s sturdy as hell. Second up it makes for ease of changes to the circuit where a PCB simply won´t stand a fighting chance in hell.
So. For someone like me,which is all about low volume,using turretboards sort of becomes a no-brainer really. I´ll never take any interest in mass production..to me it´s all about the learning curve and fooling around.
Hence why i´m not an especially "secret" guy as far as tips,trix,ideas and findings.

[Racing]

Cellphone cam still out of focus,sry about that lads. Reasoned as such that "some" picture is better than none.
That there is the stock chassis and as you can see it has been drilled into before i enter the picture.
In short this amp has seen one severe mod previous me.



So. JTM chassis. The install of the PT merely took opening the stock cutout up a bit more. In turn,as you can see,an IEC jack and atop that fuses for the HT secondary. From there in turn "saver diodes" vs the tube rectifier. It´s my finding that the use of such diodes decrease the load on the tube rectifier in a major manner,thereby elongating the life of it.



Right. Stock the output transformer is installed within the chassis right and that brings a LOT of exposed solderjoints. In this case that OT needs to swap places and thus be installed to the outside of the chassis. THAT in turn brings the need for endbells,and there´s no telling what C/C measures we´re talking right? Ie,it´s rare that "any" endbells just fit.
Had this old choke standing around from an old Vortexion choke so snagged them bells off of that. Worked like a charm.
While at it i replaced any and all wiring,for the OT and PT both.

Seing the size of the stock chassis and...now them transformers installed to a regular sized JTM chassis kind of tells the ACTUAL size of them transformers. In short they´re not overly small.

[Racing]

Must have f-d that cam lens up when i swapped the screen of the phone the other day. Whatever...

As you can see work has progressed. The choke i arrived on is of 6H which should suffice and then some.
Highpower zeners in series with a 2w 100 Ohm resistor vs each pin 4/g2,per usual.

As i scrapped the remains of the stocker i found more parts that said "France" fwiw.

Fuseholders were added,a bias board was fabbed aso. To the point where i got to fire the thing up with them two 6L6G powertubes only and a few particulars got evident.
First up i came to install a 0,33 Ohm/5w resistor for each heater winding. Made heater voltage end up just about on par.
With 340VAC inbound of the rectifier i now saw rather specific 400VDC outbound under load. Dunno about that.
Don´t get me wrong! It´ll work alright,Q of mine is to what extent. Thus i´m giving a "tube/diode" switch some thought at the moment.
Seing the voltage drop of a 5Z3 that´d bring the diode setup to dial in around the just shy of 450VDC mark,which might very well be the ticket.?

That said this thing´s coming together. Kind of raises the Q what to do of it? That last circuit of mine works very well but..it kind of gets redundant to repeat oneself over and over.
If a loop is to be in the mix a noval socket needs to be added,at the least.

Hm.

[Racing]

This time out,a little different. I´ve taken to install all components heading for ground to the sockets. Hoping to preserve space onboard the turretboards.
Might be that it won´t make for the easiest setup to service one day,then again..how often to you replace cathode resistors and/or gridleaks?



I know...i know..looks a bit clustered at the moment but rest assured..there´s a plan to the madness. As it turned out i needed to drop the voltage for the heaters a tad in 220VAC mode and..long story short-high power drop resistor-s.
Worked like a charm.
The three point switch is for speaker impedance out. IOW that´ll get installed to the rear wall of the chassis.
Wiring for g1 (negative bias voltage) is very temporary,just to get the thing up n go...so i could evaluate what i have at hand.

As is i´m trying to figure out how to handle this one. Feel like it´s time for something fresh,but...where that´ll take me is anybodys guess i suppose.

[boss302bass]

I have no idea what you're talking about, what it is, or what it's gonna end up being, but it looks cool as f**k and I hope you get it all back in that awesome looking vented black box.
I own a 400PS and I don't even look at its innards for fear it will blow me across the room.
You sir, are clearly fearless.
This thing looks like some Cheese-eating Surrender Monkeys used it in The Resistance to talk to each other behind the Nazis backs.

[Racing]

*LOL*
Nah,sry to say the stock chassis is out. For pure safety reasons really. This is the 21st century after all.



Ah! Law n order. As you can see things are starting to come together and...what can i say? From an electrical perspective it´s up and running again and B+ is all in at just a tad shy of 400VDC.
I´m not all that convinced.. Giving serious thought to replacing that 5Z3 rectifier with a GZ-34 one AND a tube/diode switch. True enough the old 6L6G´s are rated at a mere 360 volts maximum plate but in all honesty i´ve run them close to 500 on occasion with no ills and..at that voltage they´re sure handing the power.

Had to adjust a few resistor values within the voltage rail to get on mark,albeit nothing major.



One of the few "towers of power" left over from "Helmuth Kohl" way back. Have tried finding these all over the place to no avail. Hm..
Btw.
Yes. PPIMV this time out again. As always.



Preamp as of right now is three pieces of russian made 6n2p (approx ECC-808´s) and one EF-86. But i think i´ll revert to an ECC-82/12AU7 for the loop per previous builds. No reason for all that amplification in that late a stage....ECC-82 as a cathode follower outbound for the loop and then the other triode of that tube as recovery stage.
Seing the currents available from it...it is a rather safe bet as a "loop tube".

[Racing]

All that running around like a one legged chicken as far as the 5Z3 tube rectifier and B+ voltage. This is what came to be. A switch for either the 5Z3 or diodes. Take your pick and done deal.



Right. JTM-45 chassis. So. The two jacks at the end are "hi/low" right...and the other two are send/return for the loop.
Still lack pots for signal adjust for the loop. Where to put ´em though? We´ll figure that out too...



Again one of them multi way switches. Better get used to it. The use of them lets me alter capacitance inbound for the James network and in a word...it gets silly.
That there,in liason with a few other trix,makes for a width as far as amp capacity it becomes a laughing matter. From sound as scooped as you´d ever wish to downright midhump. Take your pick.

[Racing]

Bit by bit,day by day. Coming closer..



Got to stuff a SMPS transformer in there. Hands me 5VDC,which i use to run the H11 optos onboard. That "AC corner" of the amp is starting to get crowded though..

[wproffitt]

Woah! So much for law and order! You are definitely filling that JTM chassis to the gills. How much is this thing going to weigh?

[Racing]

Doubt it´ll pass 10kg all said n done.

[Racing]

...and we have life. Going to reset a few of the components. That there simply turned out to clustered. OTOH there´s quite a few gainstages at play here so...



Right. So inputjacks to the far end...hi n low...then the loop,and next to the jacks for the loop are the controls for it. Send and return. Return in practice being a gaincontrol for the PI too.

First trials tho...nah. This one doesn´t sound up to par yet. Needs work. What´s more it seems the g1´s of the powertubes crave a LOT of signal for some reason. Something´s not right here....
Yeah well. That´ll have to wait a couple of days now as we´ve got this mastodont gig coming up tonight. Gonna be onstage all in all 4+hrs... Wish me luck!