RCA AR88 LF 600 ohm - UK Vintage Radio Repair and Restoration Discussion Forum

Kevin Hoyland · 20th Jul 2017, 7:48 pm

Hello.
I have an RCA AR88 Lf. This set was rewired in the 1950s and on the back it says that the speaker output is 600 ohms and the output for the head phones is also 600 ohms. Will it be OK to use a matching transformer for the 600 ohms output so I can use 4 or 8 ohms speakers?

Thanks Kevin.

JacKam_ · 20th Jul 2017, 7:56 pm

Ok for the radio but the output power will be the same minus some loss caused by the transformer.

Station X · 20th Jul 2017, 10:35 pm

I'd be careful with the headphone connection. In some modified RCA AR88's the headphone jack was just connected to the output valve's anode via a capacitor.

turretslug · 21st Jul 2017, 1:12 am

Do you know if the output transformer is the original type? This is sealed into a round, solder sealed steel can with a square, four-hole flange and has 7 turret tags on an insulating plate underneath. The one here has RCA stock code 901666-501 (the "usual") on it but at least one other type with a different code was used, possibly with only 6 tags.

How "official" does the labelling re. impedances look? I get the impression that, by 1945, Britain was pretty much subsiding under the weight of the things and what was still an excellently specified and performing receiver thus continued in service for a long time in all sorts of places. Some had various different modifications, possibly trivial, possibly major to suit them for particular applications (some were even comprehensively rewired)- could yours have had a 600 ohm output transformer fitted for installation use? As well as the nominal 2.5 ohm loudspeaker secondary winding, the original output transformer mentioned does have a separate line feed secondary of nominal 600 ohms- if you're lucky there might just have been a bit of re-wiring around here that can be re-jigged.

Station X · 21st Jul 2017, 9:10 am

I believe the AR88 and AR88-LF used different output transformers. The output transformer of the AR88-LF was coded 901611-501.

ms660 · 21st Jul 2017, 10:35 am

Yes, also differences are shown in the E.M.E.R manual.

Out of interest, Hammond do a suitable matching transformer:

http://www.hammondmfg.com/collins.htm

Lawrence.

Kevin Hoyland · 21st Jul 2017, 10:38 am

Hello and thank you for your replys. The Photos show the output Transformer and the back of the 88lf I do not have the number for the output transformer but I will look this morning and put it on later. The mains Transformer number is 901602.
Thank you.
Regards Kevin

Kevin Hoyland · 21st Jul 2017, 10:40 am

Hello Lawrence. Yes I have been looking at that one.
Thanks Kevin

Kevin Hoyland · 21st Jul 2017, 11:41 am

Hello. The number on the output Transformer is GA3-13014 you will see by the photos that it as 12 pegs on it.

Thank You.
Kevin.

Station X · 21st Jul 2017, 12:09 pm

Not a part number I recognise.

The C.G.N variant gets a mention here:-

https://www.vintage-radio.net/forum/...d.php?t=128933

Kevin Hoyland · 21st Jul 2017, 1:40 pm

Thanks Graham.
Looking on the Radio Boulevard site it says some later AR88 Lf had a Gray panel. And looking at this one it as its original color and has never been resprayed. I will see if one of the tags on the output transformer as a 2.5 ohms reading.
Thanks Kevin.

Station X · 21st Jul 2017, 1:46 pm

I hope I'm not teaching egg sucking, but the DC resistance of an output transformer winding has no bearing on it' impedance, which depends on the turns ratio.

Kevin Hoyland · 21st Jul 2017, 2:04 pm

Hello Graham.
I will test it with a audio impedance tester to see if I get a reading.
Thanks
Kevin.

turretslug · 21st Jul 2017, 5:06 pm

12 tags sounds like there may be a few options- not that all the tags may be connected of course. I would have thought that measuring voltage ratios with LVAC applied to an ohm-meter-identified winding would be one possibility- 6.3Vac 50Hz is an easy and tempting option but might well drive too much current through a low-impedance winding and be too low frequency anyway. If you can generate 1VAC 400Hz or thereabouts into a secondary and 'scope across the other windings including primary, that could give a pointer.

I'd heard that some British-overhauled AR88s had the characteristic long chrome strips removed to assist NBC decontamination- it might even have a whisp of truth to it.... Can't be doing with all that exuberant transatlantic decor now, can we?

Station X · 21st Jul 2017, 10:27 pm

Looks like there's a 5R resistor connected to the windings. Could it be a dummy load of some kind?

G8BBZ · 22nd Jul 2017, 7:38 am

Receiver Outfit CGN was a dual diversity receiving system primarily for the reception of FSK signals and intended for use at RN Shore stations. More details at the RN Communications Museum website.
Two AR88LF's were used, in conjunction with a elaborate system of diversity switching and FSK tone demodulation. The receivers could be used in frequency or space diversity, depending on the antenna arrangement.
Facilities for AF monitoring were provided as part of the FSK demodulator, so the only audio output from the receiver was provided at 600ohm, to match the input impedance of the demodulator.
No details are given in the documentation as to the extent of the modifications performed on the AR88LF's used in this configuration, though the additional 600ohm output on the rear panel is obvious. As has already been suggested, the low impedance audio outputs may well still be there but terminated as not required in this application.
Outfit CGN was a 7ft. rack of equipment and the receivers were not provided with separate cases, so the case around this receiver would seem to be a later addition. I note from the serial number label that the receiver was refurbished in February 1956 by ATB (is this AT&E Bridgnorth?)
cheers
Peter G8BBZ

Kevin Hoyland · 22nd Jul 2017, 9:30 am

Hello Peter.
Thank you for all the information on the 88lf. I have been on the RN Communications Museum website but can not see the information regarding the Receiver outfit CGN .

Thank You.
Kevin.

ms660 · 22nd Jul 2017, 9:36 am

See post#2 here:

https://www.vintage-radio.net/forum/...d.php?t=128933

Lawrence.

Kevin Hoyland · 22nd Jul 2017, 10:25 am

Thanks Lawrence.

That' just says it all regarding Receiver outfit CGN. But I can not work out how peter can tell when it was refurbished in Feb 1956 from the ser/number I will see if I can talk with him. I can not see any information on ATB or AT@E Bridgenorth on the web.

Thank You.
Kevin

turretslug · 22nd Jul 2017, 11:17 am

That output transformer certainly looks like an excellent quality item and the fixing centres and terminal disposition suggests that it's AR88-specific. As Graham says, the presence of 5 ohms wirewound across 2 tags does raise hope of a low-impedance loudspeaker secondary as well as the 600 ohm winding(s)- the rear panel implies no less than 3 of them! I can't help wondering if these output transformers were made to order for the '50s British military at considerable expense and with plentiful spares and then, a coupe of decades on, the substantial stores holding ended up on landfill- it wouldn't be unheard of! I don't suppose it will be news to you that the once plentiful original RCA output transformers are increasingly hard to track down.

I see that the re-wiring also seems to have included lots of those white ceramic body resistors that are famous for drifting in value- the original US carbon comp types aren't great but these weren't really an improvement, I suspect that they were simply a familiar "approved" component.

Colin

20th Jul 2017, 7:48 pm	#1
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	RCA AR88 LF 600 ohm Hello. I have an RCA AR88 Lf. This set was rewired in the 1950s and on the back it says that the speaker output is 600 ohms and the output for the head phones is also 600 ohms. Will it be OK to use a matching transformer for the 600 ohms output so I can use 4 or 8 ohms speakers? Thanks Kevin.

20th Jul 2017, 10:35 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88 LF 600 ohm I'd be careful with the headphone connection. In some modified RCA AR88's the headphone jack was just connected to the output valve's anode via a capacitor. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Jul 2017, 1:12 am	#4
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: RCA AR88 LF 600 ohm Do you know if the output transformer is the original type? This is sealed into a round, solder sealed steel can with a square, four-hole flange and has 7 turret tags on an insulating plate underneath. The one here has RCA stock code 901666-501 (the "usual") on it but at least one other type with a different code was used, possibly with only 6 tags. How "official" does the labelling re. impedances look? I get the impression that, by 1945, Britain was pretty much subsiding under the weight of the things and what was still an excellently specified and performing receiver thus continued in service for a long time in all sorts of places. Some had various different modifications, possibly trivial, possibly major to suit them for particular applications (some were even comprehensively rewired)- could yours have had a 600 ohm output transformer fitted for installation use? As well as the nominal 2.5 ohm loudspeaker secondary winding, the original output transformer mentioned does have a separate line feed secondary of nominal 600 ohms- if you're lucky there might just have been a bit of re-wiring around here that can be re-jigged.

21st Jul 2017, 9:10 am	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88 LF 600 ohm I believe the AR88 and AR88-LF used different output transformers. The output transformer of the AR88-LF was coded 901611-501. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Jul 2017, 10:35 am	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: RCA AR88 LF 600 ohm Yes, also differences are shown in the E.M.E.R manual. Out of interest, Hammond do a suitable matching transformer: http://www.hammondmfg.com/collins.htm Lawrence.

20th Jul 2017, 7:56 pm	#2
JacKam_ Pentode Join Date: Jul 2015 Location: Newbury, Berkshire, UK. Posts: 243	Re: RCA AR88 LF 600 ohm Ok for the radio but the output power will be the same minus some loss caused by the transformer.

21st Jul 2017, 10:38 am	#7
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Hello and thank you for your replys. The Photos show the output Transformer and the back of the 88lf I do not have the number for the output transformer but I will look this morning and put it on later. The mains Transformer number is 901602. Thank you. Regards Kevin Attached Thumbnails

21st Jul 2017, 10:40 am	#8
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Hello Lawrence. Yes I have been looking at that one. Thanks Kevin

21st Jul 2017, 11:41 am	#9
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Hello. The number on the output Transformer is GA3-13014 you will see by the photos that it as 12 pegs on it. Thank You. Kevin. Attached Thumbnails

21st Jul 2017, 12:09 pm	#10
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88 LF 600 ohm Not a part number I recognise. The C.G.N variant gets a mention here:- https://www.vintage-radio.net/forum/...d.php?t=128933 __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Jul 2017, 1:40 pm	#11
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Thanks Graham. Looking on the Radio Boulevard site it says some later AR88 Lf had a Gray panel. And looking at this one it as its original color and has never been resprayed. I will see if one of the tags on the output transformer as a 2.5 ohms reading. Thanks Kevin.

21st Jul 2017, 1:46 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88 LF 600 ohm I hope I'm not teaching egg sucking, but the DC resistance of an output transformer winding has no bearing on it' impedance, which depends on the turns ratio. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Jul 2017, 2:04 pm	#13
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Hello Graham. I will test it with a audio impedance tester to see if I get a reading. Thanks Kevin.

21st Jul 2017, 5:06 pm	#14
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: RCA AR88 LF 600 ohm 12 tags sounds like there may be a few options- not that all the tags may be connected of course. I would have thought that measuring voltage ratios with LVAC applied to an ohm-meter-identified winding would be one possibility- 6.3Vac 50Hz is an easy and tempting option but might well drive too much current through a low-impedance winding and be too low frequency anyway. If you can generate 1VAC 400Hz or thereabouts into a secondary and 'scope across the other windings including primary, that could give a pointer. I'd heard that some British-overhauled AR88s had the characteristic long chrome strips removed to assist NBC decontamination- it might even have a whisp of truth to it.... Can't be doing with all that exuberant transatlantic decor now, can we?

21st Jul 2017, 10:27 pm	#15
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88 LF 600 ohm Looks like there's a 5R resistor connected to the windings. Could it be a dummy load of some kind? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

22nd Jul 2017, 7:38 am	#16
G8BBZ Pentode Join Date: Oct 2005 Location: Hebden Bridge, West Yorkshire, UK. Posts: 200	Re: RCA AR88 LF 600 ohm Receiver Outfit CGN was a dual diversity receiving system primarily for the reception of FSK signals and intended for use at RN Shore stations. More details at the RN Communications Museum website. Two AR88LF's were used, in conjunction with a elaborate system of diversity switching and FSK tone demodulation. The receivers could be used in frequency or space diversity, depending on the antenna arrangement. Facilities for AF monitoring were provided as part of the FSK demodulator, so the only audio output from the receiver was provided at 600ohm, to match the input impedance of the demodulator. No details are given in the documentation as to the extent of the modifications performed on the AR88LF's used in this configuration, though the additional 600ohm output on the rear panel is obvious. As has already been suggested, the low impedance audio outputs may well still be there but terminated as not required in this application. Outfit CGN was a 7ft. rack of equipment and the receivers were not provided with separate cases, so the case around this receiver would seem to be a later addition. I note from the serial number label that the receiver was refurbished in February 1956 by ATB (is this AT&E Bridgnorth?) cheers Peter G8BBZ __________________ Peter G8BBZ

22nd Jul 2017, 9:30 am	#17
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Hello Peter. Thank you for all the information on the 88lf. I have been on the RN Communications Museum website but can not see the information regarding the Receiver outfit CGN . Thank You. Kevin.

22nd Jul 2017, 9:36 am	#18
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: RCA AR88 LF 600 ohm See post#2 here: https://www.vintage-radio.net/forum/...d.php?t=128933 Lawrence.

22nd Jul 2017, 10:25 am	#19
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: RCA AR88 LF 600 ohm Thanks Lawrence. That' just says it all regarding Receiver outfit CGN. But I can not work out how peter can tell when it was refurbished in Feb 1956 from the ser/number I will see if I can talk with him. I can not see any information on ATB or AT@E Bridgenorth on the web. Thank You. Kevin

22nd Jul 2017, 11:17 am	#20
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: RCA AR88 LF 600 ohm That output transformer certainly looks like an excellent quality item and the fixing centres and terminal disposition suggests that it's AR88-specific. As Graham says, the presence of 5 ohms wirewound across 2 tags does raise hope of a low-impedance loudspeaker secondary as well as the 600 ohm winding(s)- the rear panel implies no less than 3 of them! I can't help wondering if these output transformers were made to order for the '50s British military at considerable expense and with plentiful spares and then, a coupe of decades on, the substantial stores holding ended up on landfill- it wouldn't be unheard of! I don't suppose it will be news to you that the once plentiful original RCA output transformers are increasingly hard to track down. I see that the re-wiring also seems to have included lots of those white ceramic body resistors that are famous for drifting in value- the original US carbon comp types aren't great but these weren't really an improvement, I suspect that they were simply a familiar "approved" component. Colin