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WTB Bogen M100A or Quicksilver 8417

I had the same situation before I got a pair of the MO100A.
They are very nice, somewhat larger than the MO200, but if you run a monobloc system you need to parallel the 2 power 650V HT supplies or they will run out of power.

The screen grid supply has a monster amount of current going thru it (thanks to the 8417 insane screen grid demands!) and is half wave rectified.
It's strongly advised to fit chokes in that supply to make it quieter and more stable.

The MO200 PSU transformer is the only one that was able to run 2 channels flat out without really much HT movement.

A few weeks ago several MO100A were sold quite cheaply on EBAY.
You missed them.
In my opinion that would have been your best option.

The MO200 is a bed of thorns.
Because it's much more compact it's very difficult to get rid of chassis induced hum.
The MO100A mostly doesn't have this issue, and is easier to work on.

I consider the Quicksilver a very bad clone of the Bogen amps.
It has serious stability issues and only makes about half the power of the Bogens.

The 8417 in my opinion does not work at all well in UL configuration.
Every amp like Dynaco VI, QS, all sound really lousy run like that.

The Fisher, Bogen and some others like the rarer others Mcgohan, Mac, used them in configs which were more pure pentode?

Lots of us have worked with the interesting Bogen large core transformers.
They are fantastic.

They can be made to give superb results, in my opinion WAY beyond the performance of those much hyped QS units, the only downside being the extra winding capacitances introducing higher distortion at higher frequencies compared with Fisher.
 
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john65b

Member
Paid Member
2005-01-09 2:32 am
Chicago
I cloned a Bogen M100 (QS 8417) into monoblocks, but with a few changes...used SS rectifier, separated bias control pots, used Edcore transformers, and used Tung Sol KT120s.

The 8417 was just too much trouble - always watching them to make sure they dont go into meltdown and take the amp and / or speakers with them...

I actually still have a single sylvania 8417 left if anyone is interested in it...
 
Thank you both very much for your input.
From what I have read you are both spot on.
I have read Dave Gillespie notes on his work splitting the MO200A into stereo.
That’s what I was going to base my project on.
I just picked up my 100A from eBay rather cheaply but it was boxed and shipped by a 6 year old it seems, it showed up and my house so beat up-cage smashed to bits, broken tube center pins and power switch. It was beautiful BEFORE it shipped.
The QS was only $150 , so I couldn’t resist. Outside looked rough but otherwise perfect minus the “mods” the last “audiophile” made ; )
 
abo
The 8417 was just too much trouble - always watching them to make sure they dont go into meltdown and take the amp and / or speakers with them...

I actually still have a single sylvania 8417 left if anyone is interested in it...

Sorry, this rumour about this 8417 is total nonsense.
Usual stuff was spread about with QS and Dynaco which melted the later RCA easy.

For every engineering solution there is always a solution and on the 8417 it's ultra simple.
The valve was designed for Fisher, who obviously knew what they were doing.

You HAVE to drive with a low impedance, it's as simple as that.
That was exactly what they did, so I redesigned mine with a triode connected power pentode as phase invertor, with an idle current around 20m/a, instead of the weak knee 12AU7 housed in the 7247.

That brought the 8417 drive impedance down to about 4k, with the CF side showing less than 2K.
This way they remain ultra stable, and beat anything else out there hands down.
I don't even have a bias adjuster.

QS and most of the others were absolutely suicidal letting them run at anything from 100-220k!!
They must have been nuts!

Mine are used every day, sound fantastic and use a combo of bi/tri wire which very few people have thought of to drive multiple arrays.
Only this Bogen amp allows you to do such tricks, so you connect from the 70V-115V taps, the 16-0 taps and the 70V CT taps all simultaneously to create an OPT based semi-active crossover network.

I use the 25V CT windings for CFB, with no other NFB at all.
Nobody else seems to have found this tweak, which is ideally suited to extremely hi mu valves.
It works like a charm with a simply magic sound, and there is no way you can blow it up, how ever hard you want to try.
I had lots of interraction with D.C. and we discussed many of these interesting variants.
His criticism of the OPT was based on what happens or doesn't when you load up windings..re HF distortion.
The interesting bit on the Bogen transformers is they wound all secondaries the expensive way with the same heavy gauge wire.
Once you load up the 70V, 115V sec, the thing behaves totally differently.
It's not hard to do if you are using 20-25Ohm speaker arrays.

I'll buy your spare Sylv 8417, if it's any good.
They are very difficult to make into matched pairs.

I have a pile of almost dead 8417, I rescued from different MO and MX amps.
It's suprising just how many crap or almost dead ones people are selling because they don't know how to test them! :rolleyes: (or of course don't want to because they are already DOA, but claim they're not!)
 
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