UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Testing a Mazda CRM-121 CRT with a Megger!

Lloyd 1985 · 18th Oct 2018, 12:00 pm

It's been a while, but just as an update, I got round to digging out an Ekco T161 and having a play with it, and whilst I was at it, I bunged this old CRM-121 in to see how it fared. Unfortunately at the time I had made a boo boo in the RF/IF stages, connected a cap wrong! so the picture was washed out and struggling for sync, but none the less, here's the results!

This CRT isn't staying in the Ekco, it's a bit under-rated for it, as the EHT when the sets working will be around 9-10KV, and the poor CRM-121 can only handle up to 7KV. The set was producing around 8KV when I had the tube fitted, and there was a bit of hissing and crackling going on around the neck. Needless to say, I think this tube's going to be a good one! No problems with the picture going negative at high brightness, or issues with focus.

The Ekco uses a CRM-121B, which is rated for 10KV, and I also have a Murphy V180C, which has a CRM-121B fitted, which is a good tube, and I have swapped it into the Ekco, as the one in the Ekco was rather flat. The CRM-121 that is the subject of this thread will end up in the Murphy, since the EHT for that is only 7.5KV, according to the manual. Then I will get back to the Murphy and see if I can get it going properly!

Regards,
Lloyd.

18th Oct 2018, 12:00 pm	#5
Lloyd 1985 Nonode Join Date: Jun 2008 Location: Coningsby, Lincolnshire, UK. Posts: 2,820	Re: Testing a Mazda CRM-121 CRT with a Megger! It's been a while, but just as an update, I got round to digging out an Ekco T161 and having a play with it, and whilst I was at it, I bunged this old CRM-121 in to see how it fared. Unfortunately at the time I had made a boo boo in the RF/IF stages, connected a cap wrong! so the picture was washed out and struggling for sync, but none the less, here's the results! This CRT isn't staying in the Ekco, it's a bit under-rated for it, as the EHT when the sets working will be around 9-10KV, and the poor CRM-121 can only handle up to 7KV. The set was producing around 8KV when I had the tube fitted, and there was a bit of hissing and crackling going on around the neck. Needless to say, I think this tube's going to be a good one! No problems with the picture going negative at high brightness, or issues with focus. The Ekco uses a CRM-121B, which is rated for 10KV, and I also have a Murphy V180C, which has a CRM-121B fitted, which is a good tube, and I have swapped it into the Ekco, as the one in the Ekco was rather flat. The CRM-121 that is the subject of this thread will end up in the Murphy, since the EHT for that is only 7.5KV, according to the manual. Then I will get back to the Murphy and see if I can get it going properly! Regards, Lloyd. Attached Thumbnails