PT9703 Transistor (Marconi TF2167) - UK Vintage Radio Repair and Restoration Discussion Forum

sunthaiboy · 24th Nov 2018, 6:28 pm

I am looking for a VHF power transistor part (TRW) PT9703 or a near equivalent. Does anyone have one or anything similar I can acquire?. Better still a pair as they are either in push pull or similar config (no diagram).
A helpful member from this forum has given help on this subject, but I misread the part ID. It also appears the Marconi manual shows a totally different RF Amp from the one fitted

If David reads this (who has a TRW transistor reference book), would a TPV364 do as a near replacement? The PT9703/PT9704 has a .280" 4 lead stud. A TPV365, the nearest data sheet I can find has a 0.5" stud but hopefully similar electrical characteristics. TPV365's are available at sensible money, so I was hoping to try one. A PSU failure caused a B/C short on the original.
Regards and thanks.
Robert

CambridgeWorks · 24th Nov 2018, 6:58 pm

I will try to have a look tomorrow. It sounds and looks familiar. Just need to locate the box in my garage.
Rob

sunthaiboy · 24th Nov 2018, 9:24 pm

I will keep my fingers crossed on success Rob. Thanks

G0HZU_JMR · 24th Nov 2018, 9:42 pm

I've got a TF2167 here and you can read about my exploits with the (failed) PSU here:
https://www.vintage-radio.net/forum/...d.php?t=130044

I think the PSU design is a bit of a timebomb because there are so many weak links in the PSU design. The best advice I can give you is to go over every connection in the PSU and replace all the push pin connections on the regulator PCB with direct soldered wire connections or the equivalent. The push pins on mine were oxidised and this meant I could make the PSU fail just by tapping the regulator PCB with a plastic stick. Also, I'd recommend changing all the tantalum caps in the PSU. The fuseholder had also aged and had developed an increase in ESR (so it got very hot) and also the mains 120/240V selector switch was erratic in operation.

The other thing is that the PSU absolutely NEEDS the chassis outer covers to be on because this is how it gets cooled by the fan. The air gets channelled past the PA stage via the tiny gap between the covers and the PA stage. With the covers off the fan air will just escape without reaching the PSU and the heatsink on the PSU will get to 85degC within a very short time and will probably get to 100degC if left on for a while with the covers off. With the covers on, the PSU heatsink runs at about 56degC because a small amount of turbulent air from the fan makes its way past the PA and into the PSU area. So don't run it with the covers off unless you cool the PSU with an external fan. I would strongly recommend making sure the PSU is fixed and reliable before connecting it to your amp if you get it repaired.

I still might convert the whole thing to an external 24V DC supply because I feel the PSU will one day fail and subject the PA transistors to about 40V DC from the raw rectified/unregulated output from the PSU.

On that link above Bill mentions some alternative transistors that might be suitable for the PA so this might be an option. I'm not sure which transistors are in my TF2167 but it has proved reliable now for two years and I probably use it every few months for research work here at home. It's a good RF amp when it is working!

CambridgeWorks · 25th Nov 2018, 11:55 am

Found them. These are all PT9703B. Nuts are included, the small silver blob in picture in case you wonder what it is. Leads were cut as shown in preparation for assembly but never used as product was discontinued. Original equipment was a 225-400MHz tx.
Ruler for size comparison as not sure exactly what measurement you meant.
I will pm price and then when you are sorted offer the rest in for sale section.
Rob

sunthaiboy · 25th Nov 2018, 6:25 pm

That's really great Rob. Will look out for your message

As you will see from the photo of the dead one on my opening thread, the one I removed was trimmed down quite a bit width and length wise to get them on the PCB (photo attached). They are real tricky to remove without damage to the PCB. This RF amp operates from 50KHz to 80MHz (47dB gain)
Robert

CambridgeWorks · 25th Nov 2018, 7:20 pm

PM sent.
Rob

sunthaiboy · 29th Nov 2018, 7:18 pm

Thanks to a forum member (Rob) for supplying replacement PT9703B transistors. The RF amp is now working from an external beefy 24V 5 amp PSU. I'm going to fit 4mm banana sockets and feed power externally until I can get round to designing a more reliable, less lossy, internal PSU. I think there are still issues (in-balances in the O/P load sharing) as there are different base biases on the pair of PT9703B's. The gain back up to 40+dB (running on 4V reduced input).

I still need to find the correct circuit diagram for this unit as the RF board is totally different from the one in the manual. Does anyone have one that may cover the RF amp pictured in one of the threads above (has a 1/3 of the transistor count of the one in my manual).
Regards
Robert

24th Nov 2018, 6:28 pm	#1
sunthaiboy Retired Dormant Member Join Date: Jun 2011 Location: Crew Green, Powys, Wales, UK. Posts: 68	PT9703 Transistor (Marconi TF2167) I am looking for a VHF power transistor part (TRW) PT9703 or a near equivalent. Does anyone have one or anything similar I can acquire?. Better still a pair as they are either in push pull or similar config (no diagram). A helpful member from this forum has given help on this subject, but I misread the part ID. It also appears the Marconi manual shows a totally different RF Amp from the one fitted If David reads this (who has a TRW transistor reference book), would a TPV364 do as a near replacement? The PT9703/PT9704 has a .280" 4 lead stud. A TPV365, the nearest data sheet I can find has a 0.5" stud but hopefully similar electrical characteristics. TPV365's are available at sensible money, so I was hoping to try one. A PSU failure caused a B/C short on the original. Regards and thanks. Robert Attached Thumbnails

24th Nov 2018, 6:58 pm	#2
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,859	Re: PT9703 Transistor (Marconi TF2167) I will try to have a look tomorrow. It sounds and looks familiar. Just need to locate the box in my garage. Rob __________________ Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd

24th Nov 2018, 9:24 pm	#3
sunthaiboy Retired Dormant Member Join Date: Jun 2011 Location: Crew Green, Powys, Wales, UK. Posts: 68	Re: PT9703 Transistor (Marconi TF2167) I will keep my fingers crossed on success Rob. Thanks

24th Nov 2018, 9:42 pm	#4
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: PT9703 Transistor (Marconi TF2167) I've got a TF2167 here and you can read about my exploits with the (failed) PSU here: https://www.vintage-radio.net/forum/...d.php?t=130044 I think the PSU design is a bit of a timebomb because there are so many weak links in the PSU design. The best advice I can give you is to go over every connection in the PSU and replace all the push pin connections on the regulator PCB with direct soldered wire connections or the equivalent. The push pins on mine were oxidised and this meant I could make the PSU fail just by tapping the regulator PCB with a plastic stick. Also, I'd recommend changing all the tantalum caps in the PSU. The fuseholder had also aged and had developed an increase in ESR (so it got very hot) and also the mains 120/240V selector switch was erratic in operation. The other thing is that the PSU absolutely NEEDS the chassis outer covers to be on because this is how it gets cooled by the fan. The air gets channelled past the PA stage via the tiny gap between the covers and the PA stage. With the covers off the fan air will just escape without reaching the PSU and the heatsink on the PSU will get to 85degC within a very short time and will probably get to 100degC if left on for a while with the covers off. With the covers on, the PSU heatsink runs at about 56degC because a small amount of turbulent air from the fan makes its way past the PA and into the PSU area. So don't run it with the covers off unless you cool the PSU with an external fan. I would strongly recommend making sure the PSU is fixed and reliable before connecting it to your amp if you get it repaired. I still might convert the whole thing to an external 24V DC supply because I feel the PSU will one day fail and subject the PA transistors to about 40V DC from the raw rectified/unregulated output from the PSU. On that link above Bill mentions some alternative transistors that might be suitable for the PA so this might be an option. I'm not sure which transistors are in my TF2167 but it has proved reliable now for two years and I probably use it every few months for research work here at home. It's a good RF amp when it is working! __________________ Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 24th Nov 2018 at 9:53 pm.

25th Nov 2018, 11:55 am	#5
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,859	Re: PT9703 Transistor (Marconi TF2167) Found them. These are all PT9703B. Nuts are included, the small silver blob in picture in case you wonder what it is. Leads were cut as shown in preparation for assembly but never used as product was discontinued. Original equipment was a 225-400MHz tx. Ruler for size comparison as not sure exactly what measurement you meant. I will pm price and then when you are sorted offer the rest in for sale section. Rob Attached Thumbnails __________________ Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd

25th Nov 2018, 6:25 pm	#6
sunthaiboy Retired Dormant Member Join Date: Jun 2011 Location: Crew Green, Powys, Wales, UK. Posts: 68	Re: PT9703 Transistor (Marconi TF2167) That's really great Rob. Will look out for your message As you will see from the photo of the dead one on my opening thread, the one I removed was trimmed down quite a bit width and length wise to get them on the PCB (photo attached). They are real tricky to remove without damage to the PCB. This RF amp operates from 50KHz to 80MHz (47dB gain) Robert Attached Thumbnails

25th Nov 2018, 7:20 pm	#7
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,859	Re: PT9703 Transistor (Marconi TF2167) PM sent. Rob __________________ Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd

29th Nov 2018, 7:18 pm	#8
sunthaiboy Retired Dormant Member Join Date: Jun 2011 Location: Crew Green, Powys, Wales, UK. Posts: 68	Re: PT9703 Transistor (Marconi TF2167) Thanks to a forum member (Rob) for supplying replacement PT9703B transistors. The RF amp is now working from an external beefy 24V 5 amp PSU. I'm going to fit 4mm banana sockets and feed power externally until I can get round to designing a more reliable, less lossy, internal PSU. I think there are still issues (in-balances in the O/P load sharing) as there are different base biases on the pair of PT9703B's. The gain back up to 40+dB (running on 4V reduced input). I still need to find the correct circuit diagram for this unit as the RF board is totally different from the one in the manual. Does anyone have one that may cover the RF amp pictured in one of the threads above (has a 1/3 of the transistor count of the one in my manual). Regards Robert