Ferranti 145 - it's been got at - some questions - UK Vintage Radio Repair and Restoration Discussion Forum

Gabe001 · 29th Jun 2021, 2:02 pm

Hi,

I've purchased a lovely Ferranti 145 (jelly mould), which according to the seller has been owned by her late husband who had purchased the set restored and working from a radio shop in Liverpool. The radio has worked well since purchase.

Today, I've removed the chassis in order to assess it. Apart from the purple wool (and badly frayed) dial cord I don't see any massive bodges, although some of the set's originality was rather annoyingly lost in the process. The usual caps were replaced by those grey plesseys, and some of the the electrolytics look quite modern. There are still some wax caps which will need to be replaced.

I do have a couple of quick questions and I would like to pick your brains about the following:

1. In my set, the negative pole of the smoothing and reservoir caps (c27/c28) are connected to the chassis directly, which I plan to earth. According to the circuit diagram they should be connected to the transformer HT centre tap, which is at a slightly different potential compared to the chassis by virtue of the 47 ohm resistor, R18. Is this modification likely to cause any problems?

2. Are those grey plastic plesseys innocent until proven guilty, or vice versa?

Pictures attached for reference

Thanks for your help

Gabriel

ms660 · 29th Jun 2021, 2:08 pm

The voltage developed across R18 supplies the bias for the Mixer and IF valves before the AGC kicks in, I would leave the circuit as shown in the schematic, if you connect the -ve of the reservoir and filter capacitors to chassis then all the ripple current flowing via those capacitors will also flow through R18....not good.

Lawrence.

Gabe001 · 29th Jun 2021, 2:16 pm

Yes Lawrence, thanks, that was quick!.

I know what R8 does, but why would this affect, or be affected by c27/c28?

Oh OK I just saw your extra info edit!

PJL · 29th Jun 2021, 3:29 pm

The one I restored is in this thread https://www.vintage-radio.net/forum/...d.php?t=164739. The wax caps were secured to the chassis and the electrolytics were mostly the box type clamped using straps which were missing on mine.

Gabe001 · 29th Jun 2021, 4:02 pm

Thanks PJL

I note the blue smoothing and reservoir cap bodged-in replacements when you bought the set were also connected to chassis using the tab on the gram socket.

Did you rectify this when you rebuilt the set? Also did you ever get it working with Bluetooth?

Thanks
Gabriel

PJL · 30th Jun 2021, 4:53 pm

It's wired according to the trader now, the large capacitor box that I made contains C27 and C28 and the combined -ve goes to a spare pin on the 6Q7G socket used for anchoring R18. Both R&TVS and the trader agree with this but it seems a weakness as R18 is not decoupled.

I never completed the bluetooth as it hummed like mad using the rectified LT. I was going to try an external PSU to see if that helped but never got around to it.

Gabe001 · 30th Jun 2021, 6:05 pm

Thank you. I've wired it as per trader too, replaced all the electrolytics and some of the wiring this afternoon. Turned on via lamp limiter and it seems to play well via gram. Haven't tried radio yet, mostly because I have effectively no reception in the study aka workshop. It's got good sound, but some of the components are really hard to get to. The Sobell 516 with the same valve lineup is much easier to work on.

PJL · 30th Jun 2021, 6:44 pm

Even worse when the caps are bolted down to the chassis. Mine still hums a bit more than it should. The 145 maybe a classic on the outside but nothing special inside.

Gabe001 · 1st Jul 2021, 9:41 pm

I finished the set today, it's working well on all bands and has enough gain to be driven from my phone, so should be good with a BT receiver.

I should have taken an under-chassis view picture, but I forgot and I'm not keen on taking it apart again. I mounted the replacement electrolytic caps on a tag strip and it's neater than it was.

Hum is acceptable it is only noticeable with the volume control >50% and even so you need to be standing quite close. I increased the reservoir and smoothing caps to 22/10. The rectifier can handle up to 32uf max so still well within range - in retrospect I should have gone a bit higher. Sound quality is good, slightly better than my pilot u650 but the latter is a better overall radio.

One minor thing is that the tone control doesn't seem to make any noticeable difference at all, I wonder whether this is because of the additional "fixed tone control" cap of the same value. The pot works, the wiring is correct, the resistors are the correct value and the caps are new. I can live with this; as I said it sounds good.

Quick clip of it playing through gram
https://youtube.com/shorts/dLdnEdZl4wc?feature=share

Gabriel

29th Jun 2021, 2:02 pm	#1
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Ferranti 145 - it's been got at - some questions Hi, I've purchased a lovely Ferranti 145 (jelly mould), which according to the seller has been owned by her late husband who had purchased the set restored and working from a radio shop in Liverpool. The radio has worked well since purchase. Today, I've removed the chassis in order to assess it. Apart from the purple wool (and badly frayed) dial cord I don't see any massive bodges, although some of the set's originality was rather annoyingly lost in the process. The usual caps were replaced by those grey plesseys, and some of the the electrolytics look quite modern. There are still some wax caps which will need to be replaced. I do have a couple of quick questions and I would like to pick your brains about the following: 1. In my set, the negative pole of the smoothing and reservoir caps (c27/c28) are connected to the chassis directly, which I plan to earth. According to the circuit diagram they should be connected to the transformer HT centre tap, which is at a slightly different potential compared to the chassis by virtue of the 47 ohm resistor, R18. Is this modification likely to cause any problems? 2. Are those grey plastic plesseys innocent until proven guilty, or vice versa? Pictures attached for reference Thanks for your help Gabriel Attached Thumbnails

29th Jun 2021, 2:08 pm	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Ferranti 145 - it's been got at - some questions The voltage developed across R18 supplies the bias for the Mixer and IF valves before the AGC kicks in, I would leave the circuit as shown in the schematic, if you connect the -ve of the reservoir and filter capacitors to chassis then all the ripple current flowing via those capacitors will also flow through R18....not good. Lawrence. Last edited by ms660; 29th Jun 2021 at 2:17 pm. Reason: extra info

29th Jun 2021, 2:16 pm	#3
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Re: Ferranti 145 - it's been got at - some questions Yes Lawrence, thanks, that was quick!. I know what R8 does, but why would this affect, or be affected by c27/c28? Oh OK I just saw your extra info edit!

29th Jun 2021, 3:29 pm	#4
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Ferranti 145 - it's been got at - some questions The one I restored is in this thread https://www.vintage-radio.net/forum/...d.php?t=164739. The wax caps were secured to the chassis and the electrolytics were mostly the box type clamped using straps which were missing on mine.

29th Jun 2021, 4:02 pm	#5
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Re: Ferranti 145 - it's been got at - some questions Thanks PJL I note the blue smoothing and reservoir cap bodged-in replacements when you bought the set were also connected to chassis using the tab on the gram socket. Did you rectify this when you rebuilt the set? Also did you ever get it working with Bluetooth? Thanks Gabriel

30th Jun 2021, 4:53 pm	#6
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Ferranti 145 - it's been got at - some questions It's wired according to the trader now, the large capacitor box that I made contains C27 and C28 and the combined -ve goes to a spare pin on the 6Q7G socket used for anchoring R18. Both R&TVS and the trader agree with this but it seems a weakness as R18 is not decoupled. I never completed the bluetooth as it hummed like mad using the rectified LT. I was going to try an external PSU to see if that helped but never got around to it.

30th Jun 2021, 6:05 pm	#7
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Re: Ferranti 145 - it's been got at - some questions Thank you. I've wired it as per trader too, replaced all the electrolytics and some of the wiring this afternoon. Turned on via lamp limiter and it seems to play well via gram. Haven't tried radio yet, mostly because I have effectively no reception in the study aka workshop. It's got good sound, but some of the components are really hard to get to. The Sobell 516 with the same valve lineup is much easier to work on.

30th Jun 2021, 6:44 pm	#8
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Ferranti 145 - it's been got at - some questions Even worse when the caps are bolted down to the chassis. Mine still hums a bit more than it should. The 145 maybe a classic on the outside but nothing special inside.

1st Jul 2021, 9:41 pm	#9
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,646	Re: Ferranti 145 - it's been got at - some questions I finished the set today, it's working well on all bands and has enough gain to be driven from my phone, so should be good with a BT receiver. I should have taken an under-chassis view picture, but I forgot and I'm not keen on taking it apart again. I mounted the replacement electrolytic caps on a tag strip and it's neater than it was. Hum is acceptable it is only noticeable with the volume control >50% and even so you need to be standing quite close. I increased the reservoir and smoothing caps to 22/10. The rectifier can handle up to 32uf max so still well within range - in retrospect I should have gone a bit higher. Sound quality is good, slightly better than my pilot u650 but the latter is a better overall radio. One minor thing is that the tone control doesn't seem to make any noticeable difference at all, I wonder whether this is because of the additional "fixed tone control" cap of the same value. The pot works, the wiring is correct, the resistors are the correct value and the caps are new. I can live with this; as I said it sounds good. Quick clip of it playing through gram https://youtube.com/shorts/dLdnEdZl4wc?feature=share Gabriel Last edited by Gabe001; 1st Jul 2021 at 9:54 pm.