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Project 1960s Rediffusion Reditune TP48A

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crustytv
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The heads as seen above were in an appalling state, and this must have a great part to do with the god awful sound reproduction. Yesterday I spent most of the day on and off, trying to remove 50+ years of detritus deposited on the head. This was really difficult, and I was acutely aware not to be overzealous.

I used IPA and cotton buds, going over and over the surface time after time. It took ages to remove what appeared to be calcified deposits, some were too stubborn for the bud alone. Therefore, I used a cocktail stick dipped in IPA, and then under the microscope, gently teased away at the stubborn deposits surface. Once the crud had pinged away, I then cleaned again with IPA.

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headcloseup

This has made a huge difference in the appearance of the head, and equally the sound reproduction. I still think I've got some circuits faults. The volume control seems to have little effect on the level until it's at about three quarters. If further advanced, I seem to get lots of audio interference. I think I need to get back in there, clean the volume pot and replace the rusty ge transistors.

P.s.

I forgot to say, I found a chap in the UK who offers a head relapping service. I sent him photos of the heads as they were before cleaning, he said relapping will make the head as good as when it was brand new, assuming the gap has not been compromised. This was all before I knew the outcome of the cleaning. I'll make a decision on what to do, once I've overhauled the transistors. If that improves things further, I may just leave it, if not I'll send the head off for relapping.

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Topic starter Posted : 05/03/2022 11:30 am
AncientEngineer
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Posted by: @crustytv

@ancientengineer

Hi David, the measurement is the belt laid flat as shown above, the belt was under the rulers cm measurement edge. 👍 

Apologies for delay in coming back to you, I was out all day yesterday.

I've found a belt that appears to be a good fit, laid flat (i.e. doubled & laid flat it is 210mm). If that is correct, please let me know how to get it to you.

I hope the refurbishment is progressing well, 

David.

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Posted : 05/03/2022 11:35 am
crustytv
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Hi David, I have just sent an e-mail to the address you registered with, on this forum. 👍 

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Topic starter Posted : 05/03/2022 11:43 am
crustytv
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This cannot be helping things, I forgot to look at these. Both are 20K log.

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Topic starter Posted : 05/03/2022 1:06 pm
Cathovisor
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Posted by: @crustytv

I forgot to say, I found a chap in the UK who offers a head relapping service. I sent him photos of the heads as they were before cleaning, he said relapping will make the head as good as when it was brand new, assuming the gap has not been compromised. This was all before I knew the outcome of the cleaning. I'll make a decision on what to do, once I've overhauled the transistors. If that improves things further, I may just leave it, if not I'll send the head off for relapping.

We used to have a lapping tape at work in the 80s - something we only let the S.Tel.E. of Sound Maintenance use!

I'd say once you've got it going better electronically, send the head off anyway as I can't help but feel that the surface of the head - even after your sterling effort will not be good for the tape and these days often it's the media that's more precious than the hardware.

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Posted : 05/03/2022 1:39 pm
crustytv
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Ah...this won't be helping, I failed to investigate these during the refurbish, a bit of a faux pas there. Doubt it will be the root cause of my problems, but it certainly won't be helping. Both are 20K log.

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Topic starter Posted : 05/03/2022 2:30 pm
AncientEngineer
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You're right, that definitely won't help! I'm amazed anything worked after the amount of dampness that this poor thing has endured. Could be why you had a problem with the V/C....

I'm right in the middle of a very rusty Thorn 950, & the volume & brightness controls were exactly like your two pots, water had poured down the front & CRT. The cabinet actually fell apart on me, so I had to glue it up.

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Posted : 05/03/2022 4:24 pm
Cathovisor
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Posted by: @crustytv

Ah...this won't be helping, I failed to investigate these during the refurbish, a bit of a faux pas there. Doubt it will be the root cause of my problems, but it certainly won't be helping. Both are 20K log.

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Can you dismantle and clean them up, or at least clean up and substitute the track from one of the pots into a new body? I say this because I notice one has a tapped track.

 

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Posted : 05/03/2022 4:26 pm
AncientEngineer
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@cathovisor That'll. probably be for bass correction, (Fletcher-Munson effect). Those pots are fairly standard, so you could probably do a 'cut & shut' job on them provided the track on the tapped one is o.k.

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Posted : 05/03/2022 4:35 pm
crustytv
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The pots are well past their prime, and what I assume to be the tone control appears non-responsive. As stated, they are both 20K. The volume measured OK, the tone does nothing and measures a little over 500K!!! Copious amounts of servisol injected into both has certainly improved the volume control, but nothing doing with what I assume is the tone.

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I wondered what on earth that other tag was on the other control. I certainly could do with a bit of less bass, and a bit more top end added. Sadly, that pot is toast. No idea where I'd find a replacement.

Anyway, another short video (5min) to demonstrate the progress, and if you like “The Girl from Ipanema", hang around until 1min 50-ish.

Regardless of the issues outstanding, I'm totally over the moon, and thoroughly enjoying discovering what is on all the tapes. Certainly gives what I wanted, an authentic feel to the museum.

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Topic starter Posted : 05/03/2022 4:52 pm
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Cathovisor
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Posted by: @ancientengineer

@cathovisor That'll. probably be for bass correction, (Fletcher-Munson effect). Those pots are fairly standard, so you could probably do a 'cut & shut' job on them provided the track on the tapped one is o.k.

Oh, I have no doubt that's what it's for, considering the 1µF cap connected to it seems to go to chassis - I first saw this in some late 1930s radios. One tap is nothing compared to some Grundigs, which had three taps, all with response-shaping networks connected to them.

Certainly they're an "off-the-shelf" product, made by Omeg these days but sadly, Omeg don't offer taps any more.

https://www.omeg.co.uk/potentiometers/unswitched/p20/p20-single/

 

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Posted : 05/03/2022 7:15 pm
Cathovisor
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Posted by: @crustytv

Regardless of the issues outstanding, I'm totally over the moon, and thoroughly enjoying discovering what is on all the tapes.

When you've got the Reditune(s) working tip-top, I would recommend you digitise the content for posterity. It's what I do now with all older recorded media, be it open-reel, cassettes, eight-track cartridges - especially if it's something that is unlikely to have been produced commercially or for specialised markets like the Reditune tapes.

Hard drive space is pennies these days.

As for "proper" ceiling speakers: https://www.screwfix.com/p/toa-7-ceiling-loud-speaker-6w-rms-100v-white/5518h

Even has a 100V line transformer!

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Posted : 05/03/2022 7:24 pm
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crustytv
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Spent the remainder of the afternoon being entertained by Swampy (need a new name for him now) whilst looking for 20K log pots and one with a centre tap.

Looking on a few audio fora, this centre tap arrangement seems to be referred to by some as a "loudness tap". Anyway, I found a 20K log from cricklewood for a quid! As for the 20K log centre tap, nothing. Closest I got was a 50K, with centre tap, but no idea if it is log or lin. Available from Amazon of all places.

As for speakers, I've already got two Adastra ceiling speakers, but I think I might prefer to find something more in keeping that swampy would have had. There is a youtube video of the same player, and it has the original extension speaker (see below). I might look for something similar, a wall hanging vintage extension speaker from the late 50s or 60s.

redispk

Latest pictures

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Topic starter Posted : 05/03/2022 7:29 pm
Cathovisor
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Posted by: @crustytv

Looking on a few audio fora, this centre tap arrangement seems to be referred to by some as a "loudness tap"

It is - as @ancientengineer pointed out, it's used to implement frequency response correction as described by Fletcher and Munson for low-level audio listening. In simple designs (like here) it just cuts the 'top' thus giving an apparent boost to the lower frequencies. More sophisticated systems boost both ends of the audio spectrum - on some hi-fi equipment it's labelled "loudness", others have used the words "contour" or even "shape" (I have a Marconiphone 'Unit Audio' with that on) whilst in the 1950s especially, German radio manufacturers had volume controls with it in circuit all the time.

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Posted : 05/03/2022 7:57 pm
crustytv
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Today I thought I'd take a look at a couple of tapes which appeared seized. Took one apart, and it's the pinch, I'm sure I can free this up.

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Topic starter Posted : 06/03/2022 3:56 pm
crustytv
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That didn't take too long. Pinch roller now cleaned, bearing oiled, and it runs smoothly. Cleaned the cartridge casing and repaird a couple of cracks. Replaced the green gauze, left the pressure pad as it appears to be sufficient, I do have spares. This tape is labelled as "Ballads". I'll tackle the others tomorrow.

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Topic starter Posted : 06/03/2022 4:43 pm
crustytv
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I've picked up a period portable extension speaker for the Reditune. It is very similar in appearance to the original that would have been supplied (see below).

Original Supplied Reditine Speaker

redispk

The one I've purchased is a Siemens, in green leatherette cabinet, it has a huge amount of cable, which is great as it means I can place it outside if and when I have an open day barbecue. Also, it has the correct, flat, two spade plug that matches the reditune.

Now the bit I'm unsure about, and as I've kept banging on about, I'm a total newb when it comes to audio and this matching to output TX's. The siemens has a 15ohm speaker, I'm uncertain if this will be a problem, should it be 4ohm or 8ohm?

I've read a 15ohm will be fine, in fact the amp will have an easier time of it driving 15ohm, than it would driving a 8ohm or 4ohm speaker, which is good as I want to be gentle on the amp. However, I also believe using a 15ohm will be at the expense of volume, is this the truth?

If it's a dramatic loss in volume, I'll have to swap the speaker. If it's not too much of a drop, it will be fine, after all it's for background music, not for blaring out music. I guess I have to wait until it arrives and see. I'm not too bothered if it turns out I have to replace the speaker, it's the case I really wanted, and I have speakers that could probably be installed instead, but I suspect I should use 8ohm rather than 4ohm.

As I don't have any information or specs on the Reditune, I've no idea what it would have been supplied with. Does anyone have any thoughts, any advice would be much appreciated.

The Siemens Speaker Cabinet

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speaker2
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Topic starter Posted : 07/03/2022 9:57 pm
Cathovisor
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Remind me, does this unit have 100V line output? If so, buy a transformer (CPC sell them for matching to 8/16 Ohm speakers) and fit it to the speaker. You can then play with the taps to your heart's content to get the volume you want.

A pair of AD149s will give typically 10-12W RMS output: I think there was a Wireless World design in the late 60s that gave that sort of output (I think a similar circuit is in Amos Principles of Transistor Circuits).

This looks ideal - https://cpc.farnell.com/eagle/p038/100v-line-transformer-15w/dp/LS01707

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Posted : 07/03/2022 10:22 pm
crustytv
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Posted by: @cathovisor

Remind me, does this unit have 100V line output

Hi Mike, no 100V line out on the TP48A, that was on the TP80

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I did wonder if the 15ohm speaker was a problem, whether I could use one of the two Adastra speakers I bought for the TP80 system could be used. They have tappings of .75, 1.5, 3 and 6W.

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Topic starter Posted : 07/03/2022 10:34 pm
Cathovisor
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<Looks at 2-pin DIN socket on back, slaps forehead>

Ah, right. Actually, you may find that the 15Ω speaker is a better match to the amp than you might think as often high-power stuff was intended for that impedance.

I think it'll be just fine, actually.

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Posted : 07/03/2022 10:42 pm
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