need help: substituting 1203-80 MS for ML in 100W build?

[young flower]

Hi

I´ll soon start a diy 100W amp build. I´ll use George´s instructions for the 100W kit (MetroAmp wiki) and source the parts myself (except trannies which I´m going to get from Heyboer).

As this is my first build and I have very little electronics knowledge, I planned to stick to the 100W kit instructions as closely as possible. Problem is, I´ll have to use the laydown version of the 1203-80-ML because it seems a 100W chassis for a standup PT (1203-80-MS) as shown in the kit is unavailable here in Austria.
My biggest concern with this is, that I could f**k up the PT wiring and ruin the transformer or worse. I already looked at a thread George started about the difference of the standup and laydown version: http://forum.metroamp.com/viewtopic.php?t=10971" onclick="window.open(this.href);return false;
But I don´t really understand why there isn´t any colour code indicated in the schematics for the laydown high voltage terminals - as opposed to the red full secondary and blue 80% taps in the MS schematic? And why are they reading 178 and 152V instead of Red (=500V) and Blue 80%? Are they different to the MS ones? - I don´t get it.

What do I misunderstand concerning the schematics? Do you guys think choosing the laydown version will complicate things a lot for me or should I go for it?

Thank you very much in advance
Greetings young flower

[young flower]

I would actually prefer to get a chassis for a standup PT. So if somebody knows a source in Europe - don´t hesitate to post or send me a message, I´d really appreciate it.

Thanks

[young flower]

Can really nobody help me with that?

[jimmyride]

Hi. I'm from the Czech republic. Me and my friend ordered our chassis from Ceriatone. He did the 69 plexi so he ordered a standup PT chassis version. Heyboer trannies didn't fit there though so he had to drill some more holes. I guess you could get the exact dimensions from Heyboer or the guys here and send them to Nik. Or drill the holes. No big deal at all. Nik at Ceriatone also makes pretty nice panels too. The only problem I had with them was that they were pretty thick for the potentiometers and selectors - I was able to install them but I think I'll have to change the screws for longer ones than the ones from Valvestorm. I don't think there's a better way in Europe. I guess you could also make a custom order at tube-town.net though. Or get the chassis/panels from the US.

[neikeel]

I planned to stick to the 100W kit instructions as closely as possible. Problem is, I´ll have to use the laydown version of the 1203-80-ML because it seems a 100W chassis for a standup PT (1203-80-MS) as shown in the kit is unavailable here in Austria.
My biggest concern with this is, that I could f**k up the PT wiring and ruin the transformer or worse. I already looked at a thread George started about the difference of the standup and laydown version: http://forum.metroamp.com/viewtopic.php?t=10971" onclick="window.open(this.href);return false;
But I don´t really understand why there isn´t any colour code indicated in the schematics for the laydown high voltage terminals - as opposed to the red full secondary and blue 80% taps in the MS schematic? And why are they reading 178 and 152V instead of Red (=500V) and Blue 80%? Are they different to the MS ones? - I don´t get it.

Both transformers are essentially the same (AFAIK), just wound with wires on different sides of the core for the stand up type.

You can refer to the secondary taps (ie output side):
as heaters for 6.3v (and heater centre tap) = 3 wires
bias taps = 95-105vac = 2 wires
HT wires for a dual tapped tranny = 5 wires

The HT has a centre tap = common (usually yellow, goes to the centre point of the mains filter caps).

Then two pairs of wires, an outer pair (= high voltage) and an inner pair (= lower voltage)
If you measure ac between centre tap and one of the outers you get 178vac (measuring between two outers = 356vac), measure between the inner and centertap you will get 80% of this (=152vac, or 304vac between th einner pairs). Note these are all ac volts.
Now this circuit and rectifier is a voltage doubling circuit so you get 712vac which when rectifed because of sine waves comes down to 0.707 of 712 which is approximately 500v dc, ie the quoted output for the high voltage taps, similarly 0.707 of 608 = 430v dc.

You need to decide whether you are going to use the virtual variac, the high voltage taps or low voltage taps.
Most 100w Marshalls of this era with regulated input volts matched to the impedence selector at 50Hz will give approx 490v dc on the plates of the output valves (ie using the high voltgae taps). If you use the low voltage taps for a tad over 400v there will be slightly less output, a little less clean headroom and your output valves will last a little longer (unless you use a PPIMV, in which case you are mainly driving the PI tube, no the outputs and the outputs last a lot longer any3way.

Hope that all makes sense.

[young flower]

@ jimmyride: Thanks for the input - In the meantime, I actually found a guy in Italy who makes A++ chassis .
But maybe I´ll nevertheless go with the laydown PT and TAD chassis and panels. I simply like the laydown power transformer. Gives sort of a contrast to the standup type. And the whole installation with mounting bracket and so on is kind of sexy somehow. Also gives a kind of blend between 68 and 69 chassis layout - some early 69s also had the laydown PT.
BTW: I travel to the Czech Republic sometimes and I really liked the Dobrá Čajovna tea house in Český Krumlov - and the city is beautiful of course (as many places in the Czech Republic like Praha or České Budějovice). The place changed owners some years ago, since then it´s not really the same experience any more - the former owners really spread a special aura of relaxation and calmness - but it´s still a special place. This summer, I and a friend of mine did a canoo ride on the Vltava from Vyšší Brod to Český Krumlov, was really beautiful - especially the Šumava. Greetings to you neighbour

@Neil: I understand it now. With the help of the colour chart provided with the laydown tranny it shouldn´t be a problem to install it any more. You helped me out as always here Neil - thank you very very much. I think if I couldn´t have asked you about all these things I would never have had the courage to build the plexi myself

Plexi parts - prepare to become a 69 Superbass!

[jimmyride]

I heard great things about this particular tea room as well. I never visited there though. I live too far away. On the north, near the boarder with Germany. Although I love tea. It's very tough running this kind of business. Our local tea room changed owners like... four times. One must really love it, there's no money in it at all. You seem to know a lot about Czech rep. I feel kinda ashamed by that because I only visited Austria when I was like eight years old. My friends go skiing there often. I'm not used to travel much. I haven't been anywhere for years... So... good luck with your amp! I hope you make a thread and post pics with your progress. I also made a 1968 superlead replica. I hope I'll be able to put some money together for some more amps in the future. I'd love to have one example of Marshall superlead from every era. Plus HiWatt DR103.

[young flower]

One must really love it, there's no money in it at all.

Yes - you´re probably right.

You seem to know a lot about Czech rep. I feel kinda ashamed by that because I only visited Austria when I was like eight years old.

I don´t know a lot - I´m just good at googling Czech names for places and I visited a few cities (over the course of many years) and made one canoo trip with a friend, that´s all. Please don´t feel "ashamed" that´s the last thing I want you to do ^^. In Austria - I can only recommend Vienna and maybe hiking in the mountains. Everything else is pretty small, provincial and boring if you ask me: so you didn´t miss a lot ^^.

I also made a 1968 superlead replica. I hope I'll be able to put some money together for some more amps in the future. I'd love to have one example of Marshall superlead from every era. Plus HiWatt DR103.

Ahhh yes - isn´t that what everybody wants ? I think a whole different era in my life will start with just one Superbass ! This SL/SB sound - I think it´s the sound I have been searching for since I heard a Hendrix record for the first time.
Would love to see some pictures of your 68 Superlead.

Greetings YF