Mystery ODS Tube

[ampdork]

Not to sure about IEC. AFAIK dumbles did not use IEC.
I also don't really anything there in between the screws and they are too far apart for an IEC socket. Also I see the cable in the bottom of the amp....not that it means anything of itself...Still I do not think it is an IEC...
curious...

[heisthl]

I vote for can cap - with placement there because it's using one of the 2 unused output tube holes since it's a 50 watter. The screw spacing looks right for an internal fuse block that makes the amp more idiot proof.

[UltraHookedOnPhonix]

Here's #84 (another 50W) that clearly shows a can cap in the same strange location as #175.

[IMG:800:600]http://i205.photobucket.com/albums/bb17 ... son/94.jpg[/img]

[heisthl]

This pic solves both mysteries - the output tube spacing on this one would appear to skip a hole of a chassis punched for 4 output tubes explaining the cap placement and the outlet screws would appear to be the same spacing as the ones the other one for an accessory outlet that was never punched or installed.

[UltraHookedOnPhonix]

I'm convinced!

[Funkalicousgroove]

What if any relation do the two screws on the panel above the cap or tube have?
Have not seen these screws on other ODS amps.

On the amps that used to have the convenience outlet in that location those screws also served the purpose of grounding the power cable on one side, and the .047 from the ground switch on the other. When Dumble Ditched the outlet he left the screws- they all have that.

[Runaway J]

Here's #94 (another 50W) that clearly shows a can cap in the same strange location as #175.

[IMG:800:600]http://i205.photobucket.com/albums/bb17 ... son/94.jpg[/img]

... think this is #84. If I remember it right #94 is Gregor Hildens ODS.

[ic-racer]

clearly shows a can cap in the same strange location as #175.

Good pickup. I have seen that picture may times and missed that.

[UltraHookedOnPhonix]

Even tough it’s almost certainly a can cap, I thought about how one would implement a switch to go from rectifier to Si diodes, much like some Mesa Boogie amps (if there’s a 5V tap available).

Here’s a schematic just for kicks:

[IMG761]http://i205.photobucket.com/albums/bb17 ... thGZ34.jpg[/img]

From what I’ve gathered, the GZ34 doesn’t like to see more than 60uF before the choke, the voltage will drop about 20V from normal Si diodes and using some kind of HT fuse will help keep various components safe in the event of rectifier failure. You could use a 5U4 but the voltage drop might prove to intense.

Re-biasing shouldn’t be necessary when going from Si to tube. It will be biased slightly colder than the diodes.

For all the experienced builders out there, is this something that could be implemented with concern to reliability etc.?

[heisthl]

Look at how Fender did it on the Prosonic schematic:

http://www.guitaramplifierblueprinting. ... _11x17.pdf

[Max]

Here's #94 (another 50W) that clearly shows a can cap in the same strange location as #175.

[IMG:800:600]http://i205.photobucket.com/albums/bb17 ... son/94.jpg[/img]

Hi,

As far as I remeber, this was the usual place for this can-cap for all (or at least many) of the first-generation ODS 50W (up to araound #15?, I'm getting old) .

Cheers

Max

[UltraHookedOnPhonix]

heisthl,

Thanks for the schematic! Do you know what the diodes marked D101 & D102 are doing in GZ34 mode? And what of the 8200pF caps?

[heisthl]

heisthl,

Thanks for the schematic! Do you know what the diodes marked D101 & D102 are doing in GZ34 mode? And what of the 8200pF caps?

The diodes are "cheaters" and mostly help both the regular SS side and the tube side's PIV rating (kind of like using multiple 1N4007s) and as a side benefit probably improve the rectification on the tube side.
The caps are an easy way to avoid the need for the suppressor caps to protect the diodes (and the tube I guess) from transients.

I like the way they reduced the bias by 10% in GZ34 fixed bias mode.

[UltraHookedOnPhonix]

Thanks heisthl,
Yeah, it is neat! Here's Mesa's Heartbreaker, look at page 8 for the power supply.

The bias supply looks fairly similar. No bias pot though.