Pye CTM4 line output transformer replacement. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 24th Apr 2021, 3:53 pm

Link to a previous thread about this set:
https://www.vintage-radio.net/forum/...d.php?t=146572
Murphy310's excellent Pye VT4 line output transformer substitution:
https://www.vintage-radio.net/forum/...d.php?t=178543

The plan is to use a Plessey line output transformer.
Note the position in the circuit of the boost capacitor C62. It should be possible to reposition this component to tag 9 on the transformer and the HT rail. Link tags 7 and 8 together.

DFWB.

FERNSEH · 24th Apr 2021, 4:45 pm

Wired the Plessey transformer into the Pye CTM4 and now have a healthy spark at the EY51 anode connection.

DFWB.

FERNSEH · 24th Apr 2021, 5:38 pm

Connected the scan coils to the new transformer. It's evident that the Pye scan coils are not a perfect match to the Plessey line output transformer.

DFWB.

murphyv310 · 24th Apr 2021, 6:07 pm

Just rewire the scan coils for parallel configuration rather than series David.
A few turns of wire round the core will do the AGC and Flywheel sync, mind it needs to be phased correctly, check on scope or make a 50% chance of being correct first time.

FERNSEH · 24th Apr 2021, 6:54 pm

Hi Trevor
, The scan coils in the RGD line circuit are wired in series in the same manner as the Pye VT4/CTM4. The way things are now there is just enough width with the unmodulated raster but the picture will appear smaller because of the blanking periods in the vision waveform.
Just two turns around the transformer yields 40 volts P - P, but there is considerable ringing on the waveform.

DFWB.

FERNSEH · 24th Apr 2021, 8:05 pm

The much simpler line output stage in the 14" RGD 14T.
Note the repositioned boost capacitor C45.
This is the circuit I'm using in the CTM4.

DFWB.

murphyv310 · 24th Apr 2021, 8:59 pm

What is the EHT voltage David?

FERNSEH · 24th Apr 2021, 9:31 pm

Hi Trevor,
Haven't the EHT voltage yet. I'll nip over to the shop to retrieve the Rank-Bush-Murphy EHT meter.

DFWB.

FERNSEH · 24th Apr 2021, 10:03 pm

The EHT is 12KV which is the right figure for a 14" CRT. The boost voltage measured at the first anode pin of the CRT is 320 volts.

DFWB.

murphyv310 · 25th Apr 2021, 10:26 am

Thanks David.
Two ways of increasing the width. I'd still try the scan coils parralled, a series cap to scan coils will increase width going too low will effect the "S" correction, I'd initially try a O. 22uf and see the result.
The issue of course is a mismatch between the LOPT and scan coils in the Pye.

24th Apr 2021, 3:53 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Pye CTM4 line output transformer replacement. Link to a previous thread about this set: https://www.vintage-radio.net/forum/...d.php?t=146572 Murphy310's excellent Pye VT4 line output transformer substitution: https://www.vintage-radio.net/forum/...d.php?t=178543 The plan is to use a Plessey line output transformer. Note the position in the circuit of the boost capacitor C62. It should be possible to reposition this component to tag 9 on the transformer and the HT rail. Link tags 7 and 8 together. DFWB. Attached Thumbnails

24th Apr 2021, 4:45 pm	#2
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. Wired the Plessey transformer into the Pye CTM4 and now have a healthy spark at the EY51 anode connection. DFWB.

24th Apr 2021, 5:38 pm	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. Connected the scan coils to the new transformer. It's evident that the Pye scan coils are not a perfect match to the Plessey line output transformer. DFWB. Attached Thumbnails

24th Apr 2021, 6:07 pm	#4
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,421	Re: Pye CTM4 line output transformer replacement. Just rewire the scan coils for parallel configuration rather than series David. A few turns of wire round the core will do the AGC and Flywheel sync, mind it needs to be phased correctly, check on scope or make a 50% chance of being correct first time. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

24th Apr 2021, 6:54 pm	#5
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. Hi Trevor , The scan coils in the RGD line circuit are wired in series in the same manner as the Pye VT4/CTM4. The way things are now there is just enough width with the unmodulated raster but the picture will appear smaller because of the blanking periods in the vision waveform. Just two turns around the transformer yields 40 volts P - P, but there is considerable ringing on the waveform. DFWB.

24th Apr 2021, 8:05 pm	#6
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. The much simpler line output stage in the 14" RGD 14T. Note the repositioned boost capacitor C45. This is the circuit I'm using in the CTM4. DFWB. Attached Thumbnails

24th Apr 2021, 8:59 pm	#7
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,421	Re: Pye CTM4 line output transformer replacement. What is the EHT voltage David? __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

24th Apr 2021, 9:31 pm	#8
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. Hi Trevor, Haven't the EHT voltage yet. I'll nip over to the shop to retrieve the Rank-Bush-Murphy EHT meter. DFWB.

24th Apr 2021, 10:03 pm	#9
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Pye CTM4 line output transformer replacement. The EHT is 12KV which is the right figure for a 14" CRT. The boost voltage measured at the first anode pin of the CRT is 320 volts. DFWB.

25th Apr 2021, 10:26 am	#10
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,421	Re: Pye CTM4 line output transformer replacement. Thanks David. Two ways of increasing the width. I'd still try the scan coils parralled, a series cap to scan coils will increase width going too low will effect the "S" correction, I'd initially try a O. 22uf and see the result. The issue of course is a mismatch between the LOPT and scan coils in the Pye. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member