Help diagnosing issues with a BSR TD2 portable

[HaddockLB]

Well I just had it open now and gave the record wafer switch a spray with contact cleaner. Good news is the EM87 seems to be working now. But now after recording with the mic I notice that the music I had on the tape before was still there with my voice dubbed on top. Which means no doubt the erase head is dead. Just probed it with my meter and has continuity at about 0.3 ohms. Is this normal for an erase head? Another note as well I did visually inspect the EM87's holder before the contact cleaner treatment to check for loose wires as originally suggested, found none.

[Welsh Anorak]

That's probably OK. I'd start by cleaning the record/play switch if you haven't done so yet, and give the erase head a really good scrub.

This uses the output valve as the erase oscillator driver so check the wiring hasn't come adrift. There's a small transformer in the middle of the board, so again check things are OK here - no dry joints.

[HaddockLB]

Planning to take it back up to my gramps again next week since we're going to have to actually take off the board to check the traces behind. And also I'd like to have a go at reverse engineering it to draw a circuit diagram since these TD2 machines are used with that many different board designs.

[Welsh Anorak]

Oh yes - these TD2 were married with all sorts of electronics ranging from B&O (really!) through Elizabethan and Fidelity down to the tiny firms who made a cabinet and fitted electronics of variable quality and sold them via town centre furniture stores that were everywhere in the 'Sixties.

They also were supplied to kit builders as an entry level deck.

I have a similar recorder called Dual Sound. That meant it had two speakers, not stereo, but I imagine the possibilty of misunderstanding hadn't escaped them!
The internal works look similar to yours (one PCB) so I'll dig it out and see how different it actually is.

Have a look at similar two-valve recorder circuits - there's not going to be a vast difference.

[DMcMahon]

If I am correct at Post 10 that it is a Sound A46/G2 then there is a schematic for it under the Instant Downloads via the top right corner of screen Downloads.

David

[HaddockLB]

Originally Posted by Welsh Anorak

Oh yes - these TD2 were married with all sorts of electronics ranging from B&O (really!) through Elizabethan and Fidelity down to the tiny firms who made a cabinet and fitted electronics of variable quality and sold them via town centre furniture stores that were everywhere in the 'Sixties.

They also were supplied to kit builders as an entry level deck.

I have a similar recorder called Dual Sound. That meant it had two speakers, not stereo, but I imagine the possibilty of misunderstanding hadn't escaped them!
The internal works look similar to yours (one PCB) so I'll dig it out and see how different it actually is.

Have a look at similar two-valve recorder circuits - there's not going to be a vast difference.

Mine is also marked “Dual sound” too. (Excuse my messy room too.)

[HaddockLB]

Also I think I've bought the right servicing data. The diagram does match most of the components ECL86 and EM87 but I've spotted the diagram says that the preamp valve should be an ECC83 as opposed to an ECC81 that came in my machine and what I replaced it with. Of course I know the diagram covers several variations of circuits with differences noted in the document.

[TonyDuell]

I would have expected the double triode to have been an ECC83.

[Boulevardier]

Originally Posted by Welsh Anorak

Oh yes - these TD2 were married with all sorts of electronics ranging from B&O (really!) through Elizabethan and Fidelity down to the tiny firms who made a cabinet and fitted electronics of variable quality and sold them via town centre furniture stores that were everywhere in the 'Sixties.

They also were supplied to kit builders as an entry level deck.

I have a similar recorder called Dual Sound. That meant it had two speakers, not stereo, but I imagine the possibilty of misunderstanding hadn't escaped them!
The internal works look similar to yours (one PCB) so I'll dig it out and see how different it actually is.

Have a look at similar two-valve recorder circuits - there's not going to be a vast difference.

Yes, my very first tape recorder (1962) was one of these local "tiny firm" products. It was branded "Knightrider", which strongly suggests a provenance in Maidstone - which has a "Knightrider Street" (we lived in Kent at the time), and I think it was bought through my father's works's "employee purchasing scheme". It featured the usual EZ80, ECC83, ECL82 line-up, and was decent enough with double-wound mains xformer and sturdy chassis. Its most obvious cost-saving (and space-saving) feature was the use of a neon-indicator bulb as a record-level overload indicator. For what it was, it worked well, and whetted my young appetite for tape-recorder technology.

Mike

[DMcMahon]

At Post 21 of my linked Thread at Post 10 of this Thread, I said that the Challenge schematic looked to be the same as the Sound A41 series schematic.

This also shows ECC 83 as the pre-amp valve, I believe the ECC 81 will work OK in place of the ECC 83, the ECC 81 has lower gain but maybe not really noticeable operation wise in tape recorder circuit.

David

[HaddockLB]

We had the board off and traced back components only to find all was in order. We were scratching our heads with this one until we decided to give the erase head another clean with IPA. And… Problem gone! I am surprised how sensitive tape heads are that just a little bit of leftover gunk in the wrong place can entirely disable the head.

[Boulevardier]

Well done! Now it's working, is it still using that ECC81?

Mike

[HaddockLB]

Yes. The ECC81 is still in place since when I originally bought this machine it had that valve in it which I took note of. As this was before I obtained the diagram I ordered the replacement ECC81 upon discovering the original had gone microphonic. Now upon seeing the diagram calling for an ECC83 which has me confused. Was this 81 fitted by the factory or a previous owner? In any case the machine is still working flawlessly. Additionally I’ll add that ECC83/12AX7s are a bit pricey considering people still use them to build guitar/audiophile amps with.

[Boulevardier]

Yes, I see they're £30 from Cricklewood Electronics.

[HaddockLB]

Yeah, yikes. Also couldn’t help but notice that the title has been mod edited to indicate that its a TD2, I forgot BSR was more well known for making record players as opposed to tape recorders. Funily enough if you study the TD2 you may find that BSR actually reused some record player parts such as the motor and the idler that links the motor to the takeup spool for fast forward.

[DMcMahon]

Originally Posted by HaddockLB

We had the board off and traced back components only to find all was in order. We were scratching our heads with this one until we decided to give the erase head another clean with IPA. And… Problem gone! I am surprised how sensitive tape heads are that just a little bit of leftover gunk in the wrong place can entirely disable the head.

Yes it can be surprising but not that unusual.

This is why experierenced people will often say that if cleaning heads does not fix the problem, then thougherly clean the heads again even if the heads look clean after first clean.

David

[HaddockLB]

Hi everyone. Just thought I'd come back to this thread to update you all on how my machine is doing. Well I'm pleased to say it is working perfectly. All working, Been making many recordings and playing them back. Is it normal for these kind of recorders that after being running for a while (I'd guesstimate about nearly 1 hour of playing/recording) a 50/100Hz mains buzz becomes audible from the machine, not the speakers just simply some kind of vibration from the board itself. In addition the machine begins to output a unique odour when its heated up. I am concerned if the design of this machine isn't the greatest in terms of ventillation and that the circuity could just be slowly cooking itself. The case only has a single grille at the bottom of the case and a narrow slit at the top rear. When using I actually sit the unit on top of the lid I'm unsure but I think it is designed like that so when the lid is removed and flipped the units feet snugly fit inside the lid and stop it from sliding about and also provides clearance for the bottom vent grille. Should I consider modifying my machine to improve ventillation and maybe reduce operating temperatures? I was thinking of trying to install a small fan on the bottom grille to encourage airflow through the case and over the valves.

[Analogue man]

I wouldn't stand the recorder in its own upturned lid and I also wouldn't sit it on a carpet floor either. A fan however will make a small improvement in ventilation but not a huge amount and you would get fan noise as well as the noise you are currently hearing which could be the motor (especially if the rubber grommets have hardened) or a noisy mains transformer once it gets hot.

[Uncle Bulgaria]

You can see whether the buzz is the motor or mains transformer by touching them (avoiding dangerous voltages, obviously). Often a buzz is caused by, as Analogue_man says, vibrating components from degraded absorbing materials. Tightening transformer mounting bolts, or replacing rubber mounts can solve this. Pushing on them, or poking with a wooden stick for extra safety, can dramatically change the buzz or remove it entirely, thus diagnosing the problem. Do you remember those submarine films where the engineer listens to his engine with a long screwdriver like a stethoscope pressed against his head? It's a similar process, transforming unseen vibration to a visible/audible form.

A 'speaker buzz would be more likely to be an electronic fault from filtering capacitors on the HT.

The 'unique odour' is probably the generic hot valve smell. Does it remind you of an electric fire in your grandparents' garage or attic? Most equipment of this age has a coating of greasy dust which is almost impossible to remove without careful cleaning of every surface and component. There seems to be something about valve equipment which attracts this. When they get hot, there's an indescribable (and personally not particularly unpleasant) 'unique odour', which is simply decades of dust getting toasty.

Vintage audio is not just audio, but a whole-body sensory experience.

[HaddockLB]

Alright. I will try to give them a go next time I need to open the machine up for cleaning or to fix anything else. Also got some pics to show what I meant by having it put on top of the lid along with a view of the rear vent slot I was on about when doubting how adequately ventilated this recorder is. In addition should I be concerned about any nasty substances used in these? E.g. Asbestos?