RCA AR88D Band 6 is dead - UK Vintage Radio Repair and Restoration Discussion Forum

JanWra1 · 11th Nov 2021, 10:37 pm

Hi guys

Band 6 on my AR88D is dead and I can't get it to oscillate on this band (22.5 - 32 MHz) However on band 5 (16.5 - 22-5 MHz) it oscillates at 22.5 without any hesitation. Bands 1 - 4 are also OK.
Have check all components (C30, C31, C32, l56) as well as switches and connections between the parts all seems to be OK. Both C30 and C31 are new.
What am I missing? Any advise will be appreciated

73

SM0JZT_Tilman · 12th Nov 2021, 5:12 am

May I add some snippets to this that may clarify things:
1. The VFO is fine on band 1 - 5
2. Measurements show that the Band-Switch is fine for Band 6
3. We have tried to put in a 10pF cap to temporary replace C32, this to rule out this (C32) as being defective.

So we are stuck here...

turretslug · 12th Nov 2021, 9:40 pm

Hi, have you tried another 6J5?- it may not be the problem, but quick and easy to swap. I was going to say that the plating on the adjuster rod of the piston trimmers can flake off and short against the earthed outer tube, but you've tried taking C32 out of circuit. Good luck with your fault-finding,

Colin

JanWra1 · 14th Nov 2021, 9:54 am

Hi agin
Have checked the plate voltage at V3 (pin 3) on all bands and it range from abc 110 V on Band 1 and then gradually decrease to 74 V on band 6. With V3 removed the voltage at pin 3 is 147 V. Are these figures normal?

Jan

Station X · 14th Nov 2021, 10:01 am

I've had a few problems with local oscillators running out of steam. Sometimes at the LF end and sometimes at the HF end. Fitting a new valve generally cures it and is an easy first step if you have one.

Aub · 14th Nov 2021, 10:15 am

There was an epic thread on here about an AR88 where coils had gone low Q due to the formers going porous. Could that apply to yours?

Aub

theredhouseinn · 14th Nov 2021, 11:10 am

Have a look at my previous thread on the AR88 band six problem.

John.

https://www.vintage-radio.net/forum/...d.php?t=161439

JanWra1 · 14th Nov 2021, 3:34 pm

John - your thread is really interesting and and I will study it carefully, luckily I have a full set of spare IF cans which can be used to replace the original ones after they have been checked and refurbished with new capacitors.

Jan

11th Nov 2021, 10:37 pm	#1
JanWra1 Tetrode Join Date: Jan 2018 Location: Stockholm, Sweden Posts: 78	RCA AR88D Band 6 is dead Hi guys Band 6 on my AR88D is dead and I can't get it to oscillate on this band (22.5 - 32 MHz) However on band 5 (16.5 - 22-5 MHz) it oscillates at 22.5 without any hesitation. Bands 1 - 4 are also OK. Have check all components (C30, C31, C32, l56) as well as switches and connections between the parts all seems to be OK. Both C30 and C31 are new. What am I missing? Any advise will be appreciated 73

12th Nov 2021, 5:12 am	#2
SM0JZT_Tilman Diode Join Date: Nov 2021 Location: Kungsängen, Sweden. Posts: 1	Re: RCA AR88D Band 6 is dead May I add some snippets to this that may clarify things: 1. The VFO is fine on band 1 - 5 2. Measurements show that the Band-Switch is fine for Band 6 3. We have tried to put in a 10pF cap to temporary replace C32, this to rule out this (C32) as being defective. So we are stuck here...

12th Nov 2021, 9:40 pm	#3
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: RCA AR88D Band 6 is dead Hi, have you tried another 6J5?- it may not be the problem, but quick and easy to swap. I was going to say that the plating on the adjuster rod of the piston trimmers can flake off and short against the earthed outer tube, but you've tried taking C32 out of circuit. Good luck with your fault-finding, Colin

14th Nov 2021, 9:54 am	#4
JanWra1 Tetrode Join Date: Jan 2018 Location: Stockholm, Sweden Posts: 78	Re: RCA AR88D Band 6 is dead Hi agin Have checked the plate voltage at V3 (pin 3) on all bands and it range from abc 110 V on Band 1 and then gradually decrease to 74 V on band 6. With V3 removed the voltage at pin 3 is 147 V. Are these figures normal? Jan

14th Nov 2021, 10:01 am	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: RCA AR88D Band 6 is dead I've had a few problems with local oscillators running out of steam. Sometimes at the LF end and sometimes at the HF end. Fitting a new valve generally cures it and is an easy first step if you have one. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Nov 2021, 10:15 am	#6
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: RCA AR88D Band 6 is dead There was an epic thread on here about an AR88 where coils had gone low Q due to the formers going porous. Could that apply to yours? Aub __________________ Life's a long song, but the tune ends too soon for us all.

14th Nov 2021, 11:10 am	#7
theredhouseinn Hexode Join Date: Jan 2013 Location: Kelvedon, Essex, UK. Posts: 273	Re: RCA AR88D Band 6 is dead Have a look at my previous thread on the AR88 band six problem. John. https://www.vintage-radio.net/forum/...d.php?t=161439 Last edited by Station X; 14th Nov 2021 at 11:30 am. Reason: Link added.

14th Nov 2021, 3:34 pm	#8
JanWra1 Tetrode Join Date: Jan 2018 Location: Stockholm, Sweden Posts: 78	Re: RCA AR88D Band 6 is dead John - your thread is really interesting and and I will study it carefully, luckily I have a full set of spare IF cans which can be used to replace the original ones after they have been checked and refurbished with new capacitors. Jan