Appreciate any information on EMI's 91-45 radiogram that was released in 1955. This was 'top of the tree' stuff. A PR release with front photo was in RTV&H, June 1955 on page 87 - and a link to that is here: https://www.dalmura.com.au/static/EMI%20model%2091-45%201955.pdf

There appears to be reference to the 91-45 in J.R. Publications Radio Service Handbook (R.V. Series Vol. 1, Page H74) but I don't have that handbook. Nothing in AORSM digests that I can find.

Ciao, Tim

I might have that one.

I will check out my manuals tomorrow.
Will let you know either way.

Wayne.

Thanks to Stuart Irwin and Marc, I have been able to confirm by schematic a small number of Australian made radiograms that use close variants of the original Williamson amplifier. The EMI 91-45 is the last radiogram I'm aware of that may be part of this niche group, so trying to chase a schematic to confirm it's based on a Williamson. I enjoy finding and restoring Williamson amps, and all related historical aspects.

One of the things with HMV relates to their numbering. I fixed a radio recently that was 42-71.

Now with that one the #42 was the chassis number and was used in several models. So, you may need to search for the chassis by its actual number.

Good picture of it on RM, but no schematic, just the JR reference:

https://www.radiomuseum.org/r/hismasters_true_high_fidelity_radiogram_91_45_91.html#

From that I get the strong feeling that you are looking for chassis 91.

I did not see that on a quick look at Kevin Chants site & remotely, that could be a Marconi number.

Ta for suggestions.

I had searched the AORSM HMV pages for anything related to 91 or 45 or the output stage valves (6L6G or KT66 or 807 as HMV used them for SE output stages).

Searching the AORSM data had identified that BRICO from QLD had three radiograms (chassis with radio and socket for PU):
5880 from 1948
5590 from 1949
5500 from 1950
These all have the same main amp schematic based on the original 1947 Williamson circuit but with an interesting variation of an added pre stage before the phase inverter.

HMV 91-45 Radiogram Circuit Diagram

I found it.

Will send to Brad.

Wayne.

EMI 91-45 Radiogram Circuit Diagram 1
EMI 91-45 Radiogram Circuit Diagram 2
EMI 91-45 Radiogram Circuit Diagram 3

Documents uploaded to Posts 8 and 9.

Thanks Labrat for making those scans - much appreciated.

The late 1955 schematic date, and the various modifications to the main amplifier circuit (in comparison to the WW schematics) indicates HMV spent some time and effort to modify the amp circuitry. The Nov 1955 schematic approval date is interestingly 5 months after the RTV&H product launch via EMI for marketing.

The original Williamson preamp included steep slope HF filtering at 5, 7 ,10 and 13 kHz to avoid reception and record noise, and the HMV used filtering at 4, 6 and 8kHz, as well as different roll-offs for PU, tuner and tape..

The main amp uses a 12AX7 for the input and PI stages, presumably to increase forward gain, and with likely less than 20dB feedback this would improve the main amp input signal sensitivity to match their PU/tuner/tape, but then forced them to use an elaborate coupling between those two stages to avoid LF instability. There are quite a few other subtle changes, including the use of separate cathode biasing for the output stage KT66's.

For me, the link in post #8 returns Error 404 -- file not found.

Post #9 links are OK.

Same here, link in post 8 doesn't work. Even after I added the missing "docs" folder into the URL, it still didn't work.

Link is fixed.

ZScan went to sleep during the week so I've been uploading manually and mispelt the link.

It looks like the file in post #8 had the three scans combined in one pdf. I updated the file linked in post #1 to include the scanned schematics. PS. Just saw that the post #8 link was updated.

As Marc suggested, the chassis was 91.

The EMI advert indicates the radiogram used a triple-cone loudspeaker. I guess that could have been a BAKERS Selhurst 12". PS. Rola identifies their 12-OX as having three cones - https://dalmura.com.au/static/Rola%2012-OX.PNG - although that is a nominal 2 ohm 6W speaker, and the schematic identifies 8 ohm secondary, and likely can supply 12W (so two speakers in series).