Bush DAC90A valve holders - a basic question
 

Dear members of the forum
I know that some valve holders on the DAC90A have a holding spring that must forcibly be removed prior to thinking about removing the valves. In my example below there doesn't seem to be any spring, either because the sockets are springless, or a previous owner removed them already.
I believe I can remove the valves safely, but would like to know your opinion prior to forcing or breaking anything.
Helder

Re: Bush DAC90A valve holders - a basic question
 

Hi Helder, from what I can see yours doesn't have any springs fitted. If you look at this thread https://www.vintage-radio.net/forum/...=160632&page=2 Post #33 has an image of the type of valveholder with springs, which looks different to yours. You shouldn't do any damage removing the valves, but my advice to you is if you don't need to remove them, then don't! Cheers, Jerry

Re: Bush DAC90A valve holders - a basic question
 

Thanks Jerry. I merely want to clean the contacts and socket. The radio is working pretty well after recapping, and looks cleaner than shown in the photo (taken before I started restoring it). The alignment still needs some fine-tuning. The thing is that slight wiggling of the UCH42 produces some crackling noise at the output, which in a way should be normal, but I want to rule out dirty/oxidised contacts, and I didn't yet remove any valve from the set. I also have a spare UCH42 just in case.

Re: Bush DAC90A valve holders - a basic question
 

Yes these look like springless B8A valveholders (I have seen a few).

Kinder to the valves... But take care all the same!

Re: Bush DAC90A valve holders - a basic question
 

Thanks kalee20. In the post pointed out by Jerry there are photos of both types. They're clearly different by eye. As for care, I usually do my best, but this is all new to me, so some damage is expected along the way (so far so good though).

Re: Bush DAC90A valve holders - a basic question
 

One of my 'jobs in progress' is a DAC90A. This has the springless valve holders, too. I wonder if, at some point production was switched to that type.

Re: Bush DAC90A valve holders - a basic question
 

In the Thread referenced by Jerry there are indeed photos of both types.

Post #32 shows Graham's DAC90A WITH NO springs.

Post #33 shows my own DAC90A WITH springs.

Here are my springs which I have retained, just in case ...! :)

https://www.vintage-radio.net/forum/...5&d=1526205390

Remember to pull the valves straight out of their holders - don't force them and don't wiggle!

Re: Bush DAC90A valve holders - a basic question
 

Could be. Mine is a later production model, with the perspex-backed front knobs. Although I've seen similar sockets in an older DAC90A (chassis could have been swapped with a later one though).

Re: Bush DAC90A valve holders - a basic question
 

Thanks. Definitely no springs on my set. Note taken: no forcing and no wiggling.

Re: Bush DAC90A valve holders - a basic question
 

And of course pull the valves out straight up.

Re: Bush DAC90A valve holders - a basic question
 

I removed all the valves in my DAC90A without any problems, and did so in order to be able to clean the valve pins and the sockets, besides which I was, and am, in the process of repairing the radio-replacing all the waxies, out of tolerance resistors, the o/p transformer and some of the wiring, so I thought it better to remove all the valves before undertaking what amounts to at least a partial rebuid.

Re: Bush DAC90A valve holders - a basic question
 

Everyone seems to be absolutely obsessed with replacing all the wax capacitors in these sets - why?

At this very moment as I type this post I'm actually listening to my own DAC90A radio which has been on for most of the evening and I've only ever needed to replace one single capacitor in this particular set to make it work faultlessly and reliably. Of course that particular capacitor is the "that" capacitor, ie, the output valve grid coupling capacitor, which must ALWAYS be replaced. All the other capacitors in the set are the original wax ones.

I accept that different radios sometimes need more or less capacitors replacing to get them to top performance and the amount that need replacing may also be connected with how the set has been stored over the years.

Just thought I'd better add - I've also lifted one end of the mains filter capacitor to save it from going bang, but that's it.

Re: Bush DAC90A valve holders - a basic question
 

Each to their own, Techman, but I've long regarded waxed paper capacitors in any vintage radio, etc., as 'change on sight', along with Hunts 'Moldseals', and those Black Philips things. These days I seldom check waxies, but when I do they're almost always leaky, so a blanket changes minimises the risk of a later failure, IMHO.

Re: Bush DAC90A valve holders - a basic question
 

The only places I'd leave old waxies are where the circuit impedances are low enough that dc conditions are not affected. Cathode bypass is about the only such in a DAC90(A).

This isn't very spring related!

I wonder whether the spring design went with the early metal base valves where it wouldn't do any harm and may have been a nod to high vibration applications. When the bean counters decided that all that metal was expensive, it took a while for the sockets to follow suit? Presumably sockets were never manufactured by the valve makers anyway. Except maybe Philips?

Re: Bush DAC90A valve holders - a basic question
 

Absolutely! No one is saying that they're not leaky. I think we can all agree that ALL wax paper capacitors WILL be leaky. The whole point is whether that leakage matters in the particular part of the circuit that they're in, so it's all down to understanding the circuit and whether that leakage matters. You have to ask yourself whether you're doing a 'restoration' or a 'modernisation'. These aren't a rare radio, so it actually doesn't matter too much if you get a 'joy' out of flooding the underside of the chassis with yellow, personally, I don't. In the case of my particular set, it was in such good original condition that I was tempted to not do anything to it and just keep it as an ornament, but in the end I just couldn't resist doing the minimum to make it into a good working set that could be used when necessary. The grid coupling capacitor is at the left hand end of the tag board and my repair was to remove all solder from one end of the capacitor tag and then carefully unwind its wire and bend it back out of the way behind the capacitor. I then fitted the replacement 'yellow' capacitor just behind it, so anyone looking at this set in the future will at first see the original capacitor, but then notice the replacement already in place, but not quite hiding behind it - I don't particularly believe in re-stuffing, but that's not to say that I would never do it if I thought it right to do so for a particular set. The next capacitor along, or maybe the one after that on that tag strip from memory is a screen grid decoupler. In my set this was obviously slightly leaky. I actually tested whether this leakage would affect the circuit and operation of the set due to the voltage potential across it. Its leakage made about 0.02volts difference to the screen grid voltage of that valve, also there's quite a few 'K' of resistance in series with it, so even if the leakage increased substantially, it's not going to cause any major issues other than perhaps degrading performance slightly. So if I was repairing a set like this for someone else, then I may well, with their permission, replace this one too, but certainly not on my own set. I may also consider replacing the one across the output TX, but again, not on my own set which I want to keep as original as possible, as I find an original set much more interesting still working with the majority of its original components after more than sixty odd years. I disconnect the mains filter capacitor, but leave it in place under its clamp.

As has just been mentioned, this thread is specifically about valve holder springs in these sets. I think my set had these springs, which, I of course, would have left in place as an original item fitted by the manufacturer.

As I say, each to their own with these sets. They're not a rare set so in the grand scheme of things it probably doesn't really matter what you do to your own set, as there's still going to be some mint condition examples around for those in the future to preserve as examples. At the end of the day, it's a two band AM only set, so you have to ask yourself what you're actually going to do with your set and what you're going to listen to on it after you've flooded the innards with yellow. In several years time there may not be anything left to receive on AM unless you feed it with a signal from something else, so is a total 'modernisation' of the innards really necessary, unless you just enjoy doing it of course, and who can fault you for that.

I've found a picture of my 'conservation' method of replacing the grid coupling capacitor in a DAC90A radio, just hiding behind the original, but not so far behind that it could be missed by a future restorer - shown below:-

Re: Bush DAC90A valve holders - a basic question
 

I just ease the springs out of their grooves and push them a bit up the length of the metal shroud before attempting to remove the valve.

As well as the 2 styles of base referred to, I come across a third - used by Philips - which doesn't have a spring or a 'split' in the shroud for the locating pip but instead has a raised channel the length of the shroud to accomodate the pip (which therefore only provides indexing) and punched tabs around it, which are sprung inwards to grip the flared part of the valve's glass.


As to the logic for fitting the springs - I must admit I've never heard of B8 valves working loose - if anything the various retention mechanisms are sometimes a bit too over-zealous leaving me in fear of damaging a valve when trying to remove it. At least with the old metal-shell bases used on the likes of the B8B Loctals and the B9G valves you could usually slip a screwdriver in between the base and the metal shell to ease things a bit.