2nd Generation 50W ODS Period correct Layout

[67plexi]

Good one Mike,I have a room full of amp parts I just can't find anything ?
the old lady just stacks boxes in the pathway. But she knows well to keep out of my shop and music room. Nice resistors Mike.

Steve.

[ToneMerc]

The light blue look like Mepco or Electra's.

I was searching for those but found they really aren't that great of resistors due to tolerance and drifting problems

Hmmm, they are 1% metal film precision resistors with the same RN rating as the Dale's. I guess someone should have told the military this then.

These are the same/correct resistors thats in #40.

Mepco/Electra MF7C- plates, grid bias
Mepco/Electra MF6C-cathodes
Corning MF6C- B+5
Electra RN75C- V2b output

Mike

[ToneMerc]

Good one Mike,I have a room full of amp parts I just can't find anything ?
the old lady just stacks boxes in the pathway. But she knows well to keep out of my shop and music room. Nice resistors Mike.

Steve.

Same here, I have sign over the door into my hobby room which reads "Man Room". Other than bringing me coffee, mine just usually looks in and shakes her head, although my spoiled baby girl does have a free pass to enter though.

[talbany]

I used these Mepco/Electra MF7C- on the plates... produces a real glassy slick top end..If you have some or can get em use them big part of the charm IMHO..

Tony

[ToneMerc]

big part of the charm IMHO..

Tony

Along with the Piher carbon films according to another of our resident experts.

[Structo]

Sorry I didn't mean to sound critical of your resistors Tone Merc.

Something I thought I had read about the light blue resistors.
I can't find it now so I may be mistaken.
It was something about the Temperature Coefficient being poor.
This was with resistors that were before the RN specifications.
When the M10509 designation was used it was found that some manufacturers were not meeting specifications and so a different system was devised with much more stringent testing.

Abuse of the M10509 marking resulted in legal action. In 1982 it became law that all M10509 qualified parts must have JAN on them. Misuse of the JAN (Joint Army Navy) logo is an offense punishable by law.

Electra made resistors for the US military as far back as 1956. Electra was a major supplier for military parts until acquired by Mepco. Mepco acquired Electra in the early 1970s. At that time Mepco was a North American Philips Company. Mepco was Mepco/Centralab by the late 1980s. In the early 1990s the name was simply Philips. M/E (Mepco/Electra) denotes that the part was made after the acquisition of Electra by Mepco.


Interestingly, the RN65D designation does not mean a resistor is metal film. Until the 1970's the RN65D resistors were very often carbon film.

[img768]http://www.33audio.com/enter/pics/60D.jpg[/img]

[img768]http://www.33audio.com/enter/pics/65D.jpg[/img]

[ToneMerc]

No worries, my point was that your statement contradicts what on my 1970 Electra MFxC datasheet and whats written on the resistors as well.

RN rating

http://www.logwell.com/tech/components/ ... stors.html

Here's an Mepco datasheet that I found on 33audio as well.

http://www.33audio.com/enter/data/electra.pdf.

From 33audio site
An MF7C is an Electra RN70D without the large military package. The resistive element is the same as an RN70D. TCR is 100ppM/deg C. Some have T-0 as the TCR code. Some have D as the code.

An MF6C is an Electra RN65D without the large military package. The resistive element is the same as an RN65D. TCR is 100ppM/deg C. Some have T-0 as the TCR code. Some have D as the code. TCR is Temperature Coefficient of Resistance.

Well, time to melt some solder.

Mike

[marcos]

Hi everyone,
a little more on this:My personal amp (2nd generation, #4x) was finished
on May 11th, 1979, according to HADs signature inside the amp, and delivered in June 1979.Later that year I saw the first 3rd generation amp
with the toggle switches, so I believe the transition took place in 1979.
Also, my amp has the RG 59, solid core coax.
The Middle pot is a 250 KA 10% taper,FWIW

Marcos

[Structo]

Hi Marcos,

Please excuse me if you have mentioned this before but did you have Alexander Dumble build this amp for you personally?

I believe you have said you live in Italy?

I'm just curious how you came to acquiring your amp since we have all heard the stories how you had to qualify for HAD to build you an amp.
Are you a pro musician?

I don't mean to pry so if you would rather not say that is fine as well.

[talbany]

Hi everyone,
a little more on this:My personal amp (2nd generation, #4x) was finished
on May 11th, 1979, according to HADs signature inside the amp, and delivered in June 1979.Later that year I saw the first 3rd generation amp
with the toggle switches, so I believe the transition took place in 1979.
Also, my amp has the RG 59, solid core coax.
The Middle pot is a 250 KA 10% taper,FWIW

Marcos

marcos
Thanks for your comments..As always your input here is greatly valued!!

Tony

[Max]

Hi everyone,
a little more on this:My personal amp (2nd generation, #4x) was finished
on May 11th, 1979, according to HADs signature inside the amp, and delivered in June 1979.Later that year I saw the first 3rd generation amp
with the toggle switches, so I believe the transition took place in 1979.
Also, my amp has the RG 59, solid core coax.
The Middle pot is a 250 KA 10% taper,FWIW

Marcos

Hi Marcos,

AFAIK the very last of the 2nd generation "pre-classic" amps, which, like yours perhaps, too, are already equipped with the 3rd generation black RG59/U foam, have indeed been completed and signed in 1979. But AFAIK at least around 90% (please read as "the vast majority") of the 2nd generation amps have been built in the years Tony posted (1975 – 1978). Of course there are always some late ones and some early ones concerning "production year dates". Or do you know many more 2nd generation ODS with a 1979 signature and the 3rd generation RG59 coax cables?

10% taper 250KA mid pot:

This is interesting that you know at least two amps (your own 2nd generation and this single 3rd generation) with a 10% taper 250KA mid pot. Could you perhaps post what precisely is all stamped into or written on this mid pot in your own amp, which you did measure to have a 10% taper?

RG59 coax in your own 2nd generation ODS:

If I understood correctly what you’ve posted, your 2nd generation "pre-classic" is not equipped with the usual 2nd generation grey Columbia Flexfoam coax cable (like #040 as an example) but with a RG59 coax cable. This is interesting, too. Is there anything written on the RG59 cable in your amp, be it a brand name or something else? And what is the sheath colour of the RG59 in your 2nd generation amp? And do you know the specs and dimensions (AWG or mm) of its core, its dielectric isolation and its sheath?

Thanks again for all your valuable contributions, especially concerning this 2nd and 3rd generation "pre-classic" ODS topic.

All the best and have a great day,

Max

[EaNot]

Anybody can draw and place the scheme exactly this versions? Not a layout.
Beforehand thank You!

[ToneMerc]

Anybody can draw and place the scheme exactly this versions? Not a layout.
Beforehand thank You!

Here is a Layout of a period correct 2nd Generation ODS 50W specimen,complete with part numbers for cap types, resistor types, type coax with specs, FET # for cross referencing and other valuable info.. If you have any questions please feel free to ask. However the source of this info and the series # of this amp and its whereabouts etc must be kept confidential due to request, so don't ask for pictures, Schematics or relevant information pertaining to this particular amp here or in a PM..Thank You!!

TM

[marcos]

Hi Tom,
just a quick one:I am from Germany, and a number of Dumbles were imported by Applied Acoustics, who later on built Kitty Hawk amps.These amps were for sale in a number of shops here in Germany, so you did not have to qualify for a build.
However, I must add that I had several requests to HAD by letter,
and he answered each one competently and politely, and free of charge.

Hope this answers your questions Marcos

[ToneMerc]

"so you did not have to qualify for a build.
However, I must add that I had several requests to HAD by letter,
and he answered each one competently and politely, and free of charge.

Same experience here back in 89', as he was real cool in the beginning of the deal. It was the 4th or so phone call that he threatened to charge me.

TM