UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

beery · 10th Nov 2018, 9:13 pm

Hi all,

regarding CRT substitution, see post 23 on page 2 of this thread:-
https://www.vintage-radio.net/forum/...=118931&page=2

I'm already testing with a Russian 18ЛК5Б CRT. It seems the best fit really, especially as it has an ion trap.
Another posibility was the 7BP4, but this CRT is hard to find.

I actually managed to import two of the Russian CRT's. The second one I obtained was actually NOS and I passed it on to Mikey405 for his EKCO. I've been trying to get another CRT over since then, but the only lead I did have fell through.

Due to the trade restrictions with Russia, I have had to get the tubes from the Ukraine, but they are harder to find over there. Perhaps someone fancies a road trip to Russia to pick up a few CRTs?

Generally prices for the 18ЛК5Б CRT go up to about £30 plus carriage. It is not worth breaking up a KVN49 for a CRT (surely a crime?) as even the roughest sets seem to be expensive. The KVN49 is not rare, but it has become very collectable in the countries in which it was used...

Anyway, I digress. Back to the HMV 905. I do hope the CRT is not gassey and there is no easy way of checking it out. Maybe I have to bodge the CRT into my TV22.

Regarding the interlace, a good spot, but not something I'm concerned about just yet. It might be due to the setting of the synch control which on the face of it (without checking for interlace) seems to do nothing.

When I first rebuilt the set I did indeed align it using the method in the manual, but as the IF coils are so heavily damped it was hard to know where the sweet spot for each coil really was. Hence I purchased the signal generator with a mind to do a better job of it. Frequency markers are not really necessary due to the fact that the signal generator is digitally synthesising the frequencies and so its output will be perfectly linear. There is however a slight roll off in amplitude in the VHF range due to the signal generator's output stage, but if I actually inject it into the IF amplifier with a centre frequency of 8MHz then its output will be very much the same across the IF bandwidth.

I've been under the weather the last few days with silly cold, but hope to get back to the set soon.

Cheers
Andy

10th Nov 2018, 9:13 pm	#174
beery Heptode Join Date: Jun 2006 Location: Ware, Hertfordshire, UK. Posts: 988	Re: HMV 905 Project Hi all, regarding CRT substitution, see post 23 on page 2 of this thread:- https://www.vintage-radio.net/forum/...=118931&page=2 I'm already testing with a Russian 18ЛК5Б CRT. It seems the best fit really, especially as it has an ion trap. Another posibility was the 7BP4, but this CRT is hard to find. I actually managed to import two of the Russian CRT's. The second one I obtained was actually NOS and I passed it on to Mikey405 for his EKCO. I've been trying to get another CRT over since then, but the only lead I did have fell through. Due to the trade restrictions with Russia, I have had to get the tubes from the Ukraine, but they are harder to find over there. Perhaps someone fancies a road trip to Russia to pick up a few CRTs? Generally prices for the 18ЛК5Б CRT go up to about £30 plus carriage. It is not worth breaking up a KVN49 for a CRT (surely a crime?) as even the roughest sets seem to be expensive. The KVN49 is not rare, but it has become very collectable in the countries in which it was used... Anyway, I digress. Back to the HMV 905. I do hope the CRT is not gassey and there is no easy way of checking it out. Maybe I have to bodge the CRT into my TV22. Regarding the interlace, a good spot, but not something I'm concerned about just yet. It might be due to the setting of the synch control which on the face of it (without checking for interlace) seems to do nothing. When I first rebuilt the set I did indeed align it using the method in the manual, but as the IF coils are so heavily damped it was hard to know where the sweet spot for each coil really was. Hence I purchased the signal generator with a mind to do a better job of it. Frequency markers are not really necessary due to the fact that the signal generator is digitally synthesising the frequencies and so its output will be perfectly linear. There is however a slight roll off in amplitude in the VHF range due to the signal generator's output stage, but if I actually inject it into the IF amplifier with a centre frequency of 8MHz then its output will be very much the same across the IF bandwidth. I've been under the weather the last few days with silly cold, but hope to get back to the set soon. Cheers Andy __________________ www.youtube.com/user/andyvalve100