FW: [AMPS] 8877s and MRIs?

[Richard W. Ehrhorn]

Barry...

ETO 16 kW (peak) amps used in virtually all GE, Picker, Philips & Toshiba 
1.5 Tesla MRI systems from 1984-89 were servo-tuned and bandswitched with 
digital stepping motors. They used a pair of 8877s. Quite a few of the same 
amps also were used in smaller Philips systems - down to 0.5T. After 1989 
GE changed to single frequency amps using one 3CPX5000A7 (3CX15000B7 with 5 
kW cooler) or YU-, YC-, etc "special or private version" equivalents. I 
think most Philips and Picker 1.5T systems followed suit by about 1990-91, 
'though a trickle of the 2x8877 amps was delivered until fairly recently. 
New, single-frequency amps of single-8877 design have recently gone into 
service in the same general range of system sizes, by one or two of the 
above companies other than GE. Sorry, I can't be more specific.

So far as I know, Siemens is the only major high-field (1.0-2.0 Tesla 
magnets) MRI supplier that never used 8877 amps; they evidently made their 
own at first, and later have had a captive (?) supplier. Think they also 
were the only major outfit to use tetrodes (big ones).

Less well know companies (e.g., Israel's Elscint) made some high-field 
MRI's, too, and quite a few other companies made mid- and low-field models 
- 0.5T down to 0.03T or so. Most of the latter probably had rf amps of 1 kW 
or lower peak output. I'd hazard a guess that GE, Picker, Philips & Siemens 
have accounted for 90+% of the world high-field market from the mid-80s to 
present. Market share evidently has shifted quite a bit recently, but it's 
doubtful that the group of major players has changed. Finally, I think most 
of the GE 8877 amps were surplused-off during the mid-90s - various 
chasses, parts and assemblies have shown up all over the ham surplus 
market.

Good luck -- and watch out for 8877s with the '87-89 code dates that I've 
warned about on the reflector. They should be long gone by now in any case. 



-----Original Message-----
From:	Barry Kutner [SMTP:w2up@mindspring.com]
Sent:	Saturday, May 08, 1999 10:57 AM
To:	amps@contesting.com
Subject:	[AMPS] 8877s and MRIs?


Does anybody know which MRI units use 8877s? How often dso
they replace the tubes? I'd like to be able to find a pull at our local
hospital/MRI Center if possible...
Tnx/Barry
--
Barry Kutner, W2UP              Internet: w2up@mindspring.com
Newtown, PA         FRC         alternate: barry@w2up.wells.com

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