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Old 1st May 2021, 7:11 pm   #21
kirstyd
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Default Re: Ferguson 401 radiogram

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Originally Posted by ms660 View Post
A general rule of thumb for the ripple current rating for a reservoir capacitor (the one connected directly to the cathode) is that it should be at least twice the DC load current.

The maximum reservoir capacitance given in the GZ32 valve data is 60uF providing the total series resistance is a minimum of 150 Ohms:

http://www.r-type.org/pdfs/gz32.pdf

Lawrence.
thanks Lawrence
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Old 9th May 2021, 10:06 pm   #22
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Default Re: Ferguson 401 radiogram

Hi again.

I seem to have the amplifier working well now. After changing the caps and some bad resistors it's running nice and cool. The mains transformer is just warm in fact the only thing hot is the two large green resistors, but even those are not hot enough worry about. Today I have started on the tuner replacing the wax covered caps one at a time testing in between. There's just the two in the photos to do. Can you tell me if the aluminium one with the black band round one end is an electrolytic and any advice on the other one would be appreciated. I have also replaced the wax caps on the control panel. I have to say it sounds very nice even with the speaker just propped up on the bench. Nice clear sound on FM but also plenty of Bass. I think it will sound rather good once it's all back in the cabinet.
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Old 9th May 2021, 10:19 pm   #23
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Default Re: Ferguson 401 radiogram

The first one is a paper wax capacitor capacitor, Modern Polyester types will work just as well. RS and Farnell stock them.

The second is an electrolytic 4.7uF/150V it's used in the FM detector, the voltage across it wouldn't normally exceed 50V-60V. so you can use a 100V type.
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Old 10th May 2021, 10:11 am   #24
kirstyd
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Default Re: Ferguson 401 radiogram

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The first one is a paper wax capacitor capacitor, Modern Polyester types will work just as well. RS and Farnell stock them.

The second is an electrolytic 4.7uF/150V its used on the FM detector, the voltage across it wouldn't normally exceed 50V-60V. so you can use a 100V type.
Thanks Maurice .I wasn't sure about the paper one
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Old 13th May 2021, 9:30 pm   #25
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Default Re: Ferguson 401 radiogram

Well i think this is ready to go back into its cabinet. After changing a hand full of wax caps /some electrolytics and quite a few resistors also one of the EL84's gave up the ghost [replaced it with another ] I had it running on Radio 2 all Saturday afternoon with nothing getting hot. It's not as loud on FM as it is on MW or long there's even a few stations on SW.

The Collaro Challenger is now running as it should and has been fitted into the cabinet. I made a new base board [ that fits over the existing one ] and covered it in some cream Rexine. It's not a bad match. The cabinet has been stripped and refinished. The bars on the speaker grille and the base board have been resprayed. [The brown paint took some finding]. Inside where the amplifier sits has just 6 small holes for ventilation so I am going to mount the amp on two blocks of wood lifting it up and allowing more air to circulate. The magic eye is quite dim but replacing it is far too expensive so it will have to stay as it is for now. Will be nice to get it back together and see how it performs.

K.
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Old 13th May 2021, 9:32 pm   #26
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Default Re: Ferguson 401 radiogram

This is where the amplifier would normally sit
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Old 14th May 2021, 9:39 am   #27
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Default Re: Ferguson 401 radiogram

Maybe open those vent holes right out and fit a suitable finger proof wire mesh sandwiched between the chassis and cabinet?

Though if it's all survived this long with no obvious heat damage it's probably fine as it is.
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Old 14th May 2021, 3:27 pm   #28
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Default Re: Ferguson 401 radiogram

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Maybe open those vent holes right out and fit a suitable finger proof wire mesh sandwiched between the chassis and cabinet?

Though if it's all survived this long with no obvious heat damage it's probably fine as it is.
Yes I did think the same but then again more air flow can't do any harm. Not bothered about anyone touching anything while switched on after all you would have to move it away from the wall and then tip the thing up before you could touch any live parts.
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Old 18th May 2021, 8:47 pm   #29
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Default Re: Ferguson 401 radiogram

just a last question about this before its finished .there is a capacitor across the speaker arrangement that seems to have a crack along its side .should i replace it or leave it [both speakers are working]
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Old 19th May 2021, 8:57 am   #30
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Default Re: Ferguson 401 radiogram

I think that's just the moulding. If you replace it, use a non-polarised 2.2uf. Unusual to see those 2 resistors in the filter circuit, but suspect that the Plessey 6" x 4" driver is used more as a Mid/High unit than as a Tweeter per se.
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Old 19th May 2021, 9:48 am   #31
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Default Re: Ferguson 401 radiogram

It's a judgement call.....

It's a notorious old Hunts one, renowned for going leaky, but where it's at, unless it's gone open circuit or dead short, it's unlikely to make much difference to the operation of the circuit.

The audio amp is rather interesting..... direct coupling and a self phase splitting long tailed pair output stage!
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Old 19th May 2021, 7:45 pm   #32
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Default Re: Ferguson 401 radiogram

i replaced the cap with a 2.2 Uf and now the sound from the small speaker is much brighter making quite a difference in the overall sound . can you please explain about the amp [direct coupling / self phase splitting /long tailed pair ] as i said at the beginning i am a bit of a novice
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Old 19th May 2021, 9:15 pm   #33
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Default Re: Ferguson 401 radiogram

Hmmm....

Direct coupling means that there is no capacitor (there may be resistor(s)) between the anode of the audio preamp valve and the grid of the output valve, in this case one of the output valves. In this set, there is no explicit phase splitter circuit to provide inverted and non inverted drive to the output valves, they act as their own phase splitter as follows:

The first output valve, V7 has its grid driven directly by the preamp valve, V6 producing an anode signal inverted vs its grid signal. The second output valve, V8 has its grid held at the same dc level as V7's via R113 but no signal reaches it since it is ac grounded by C108. The common cathode resistor R110 (the long tail), both raises the common cathode voltage high enough so that it is positive vs the anode voltage of V6 providing the right bias conditions for the output valves and couples an in phase and (nearly) equal signal voltage to that at the grid of V7 onto the cathode of V8. Since V8's grid is (signal) grounded this causes V8's anode to produce a signal of the same level as V1's but in phase with the grid signal at V7. So the two output anodes' signals are in opposite phase same as in a more typical p-p output stage. They are combined in the output transformer as usual to drive the loudspeaker.

The system saves a valve (or at least half of a double triode) at the expense of slightly more complex design and susceptibility to component drifts and may offer some stability benefit for the negative feedback loop.

HTH.....

Others may well put it more clearly!
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Old 19th May 2021, 10:26 pm   #34
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Default Re: Ferguson 401 radiogram

Thank you for the in depth explanation .I have read it three times and i think i understand . I replaced about five resistors on the amplifier .some were high and two were open circuit R113 being one of them .When i fitted the new on the volume was considerably increased
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Old 19th May 2021, 11:20 pm   #35
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Default Re: Ferguson 401 radiogram

The output stage design wastes a lot of HT that could have otherwise be used to generate output power. The cathodes of the EL84s sit up at 78V.

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Old 25th May 2021, 9:21 pm   #36
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Default Re: Ferguson 401 radiogram

The radiogram is now finished although FM is a bit quiet [need volume up full to get reasonable listening level] its working very well .and the Collaro deck is a good match for the age of the unit although it took some fiddling to get it working properly [fascinating to watch] I also made a new turntable mat after seeing another members thread on the perfect thing from that well known Swedish supplier [i bought 10] they are perfect for the job but don't draw on them with a pencil its practically impossible to get off . the amplifier has been cleaned and is now sitting on its raised up blocks giving much better air flow. I like to keep original mains leads where possible but this one had been cut very short so i replaced it with a decent length . The 401 was made in 1955 meaning it was already 2 years old when i was born .
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Old 26th May 2021, 8:40 am   #37
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Default Re: Ferguson 401 radiogram

That looks super and what a lovely veneer. The mono-only cartridge in your re-claimed Collaro "Conquest" should be a Collaro Studio "O". If it is a Studio "T", it may overload the amplifier. In terms of weak FM, a possible quick fix might be the change the ECC85 for a known good valve.
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Old 26th May 2021, 9:21 am   #38
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Default Re: Ferguson 401 radiogram

Looks great!

Also who's the "famous Swedish supplier" of those mats? too cryptic for me... Ikea?
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Old 26th May 2021, 10:23 am   #39
kirstyd
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Default Re: Ferguson 401 radiogram

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That looks super and what a lovely veneer. The mono-only cartridge in your re-claimed Collaro "Conquest" should be a Collaro Studio "O". If it is a Studio "T", it may overload the amplifier. In terms of weak FM, a possible quick fix might be the change the ECC85 for a known good valve.
Hi Edward .yes the cartridge is a model O .It seems to be ok but up to now i have only played a couple of 78s on it just to test the deck out [i got the Collaro working well but when in the cabinet the speed change knob wouldn't move it was being jammed by part of the old plinth underneath once some of the wood was removed everything was fine] .As you know i am limited as to what i can play due to the cartridge not being stereo compatible and as the cost of two mew needles for it are going to cost the thick end of £20 i may just fit one of those cheap foreign ones [they do seem to work well].As for the weak FM i have tried another ECC85 no change .I think realignment may be needed as the top end of the scale is practically dead on all wavebands [a bit beyond me and i dont want to make it any worse than it is]
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Old 26th May 2021, 10:25 am   #40
kirstyd
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Default Re: Ferguson 401 radiogram

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Looks great!

Also who's the "famous Swedish supplier" of those mats? too cryptic for me... Ikea?
You got it .I must say i am delighted with the replacement mat [must get a few more before they stop making them ]
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