Bush AC11 This Capacitor that needs replaced?

[Morayfirthaudio]

Hi again 😀 So I’m chuffed that I can get my old Ecko U109 looked at, but the issue I have at the moment is that I have an old Bush AC11. This came to me original, complete with 2” of dust. The owner says it works, so when it arrived, with some trepidation I plugged it in and......... it worked! Whew!!
But I’ve been reading about this capacitor that needs replaced!
I’m a deacon with a soldering iron, but I don’t want to make it look like I’m some electrical wizard because I’m not really. So would you mind pointing this thing out and what value does it need to be?
Secondly, as this is an old girl I thought it would be safe with an earth lead as well, so is it a case of bolting it to the Aluminium chassis, or is there a better place?
Thanks once again for any help

[TrevorG3VLF]

The capacitor is connected to the grid, pin 6, of the output valve, UL41.
This is numbered C29 on the Trader sheet and C33 on the manufacturers sheet.
Value is 0.01uF = 10nF. Voltage rating at least 400V.

Snip the old capacitor off leaving some lead connected to the set. Wind a small helix on each new capacitor lead, I use a small watchmakers screwdriver. Place the helix over the old dog end and solder on. It is difficult to remove the old leads from the set so this method avoids damage.

The position of the earth will depend on the level of interference coming in on the earth lead. There are regulations to do with house internal earths and external earths. They can be at substantialy different voltages.

[cathoderay57]

Well, answers to your specific questions are given below, but first it is worth asking another question. Has any obvious restoration work been done on the AC11 recently or at all (replacement components)? If not, then simply replacing one capacitor and adding an earth lead (while definitely worth doing) would really only be part of the job if you want the radio to perform reliably for several years at least. A proper check over along the lines shown here https://www.vintage-radio.com/repair...and-tests.html is strongly recommended. Also, so that we are all singing to the same hymn sheet the following component idents refer to the Trader Sheet #951 that you can purchase here https://www.service-data.com/product.php/701/901/t10701 . If you get the Manufacturer's service sheet, while the component values will be the same, the component ident numbering is likely to be different which can lead to confusion. OK - the capacitor I think you are talking about is C29 (0.01uF or 10nF which is the same). Voltage rating 300v minimum. Connected between the anode (pin 2) of UBC41 and resistor R19 (47k) connected to grid1 (pin 6) of the UL41. Earthed lead - you need to be absolutely sure that you have the AC11 model (and not the DAC11). If yours is the AC11 then the mains lead will be connected via the on-off switch to a transformer. Although the valve heaters on the AC11 are in series chain (similar to an AC/DC set) they are wired to a high voltage secondary winding on the mains transformer, so it acts as an isolating transformer and therefore it is safe to connect an earth lead to a convenient point on the chassis. Hope that helps and good luck. Cheers, Jerry OOops, crossed in the post with Trevor

[Morayfirthaudio]

Brilliant guys, thank you.
I’m working on the Trader sheet 951, so that’s fine.
TrevorG3VLF, totally appreciate the message, I’m a bit list on the terminology but I’ll work out.
Cathoderay57, much obliged. I think your right. This is truly a lovely piece of kit and needs to earn its keep by working most days, so I think a closer look at replacing bits and bobs. Where my knowledge falls down is making sure I have the correct components and they are not going in backwards or back to front.
I’ll try an Earth on the chassis, if I get a hum I’ll remove it. I’ll order the main capacitor now and get this bit done at the weekend and I’ll check the overhaul link and do a little bit at a time
Much appreciated ��

[Morayfirthaudio]

Oh! It’s definitely an AC11, totally positive

[TrevorG3VLF]

What terminology causes you problems?

The grid capacitor is not polarity sensitive and so can be connected either way round.
There are electrolytic capacitors in the HT supply, these must be connected the right way. These can 'go off'with time and ideally need reformig, perhaps this has already be done by turning on for a time. If they do not reform, there may be a lot of hum and if they leak may cause excess strain on other components.

[Morayfirthaudio]

Hi TrevorG3VLF, just getting my head around the helix that’s needed, if I see it it’s Ah! Got it! But I can’t see it in my minds eye..
There is no hum at all with this set, it performs perfectly.
When I typed in the capacitor needed, there is about a dozen different shapes and sizes so I’m not keep on chucking anything in even although it’s the correct value. So I’ll need to dig a bit deep to make sure I’m getting it right. I did see a link to CPC for a capacitor but the link is dead so I’ll need to do a bit more homework

[Herald1360]

Originally Posted by Morayfirthaudio

Hi TrevorG3VLF, just getting my head around the helix that’s needed, if I see it it’s Ah! Got it! But I can’t see it in my minds eye..

If there's enough lead left from the old capacitor after its removal by cutting the wires close to the body, they can be formed into small helices of iside diameter slightly greater than the leads on the new capacitor by wrapping round a suitable drill bit or jeweller's screwdriver etc. The leads of the new capacitor (whose body will likely be quite a bit smaller than the old one's) can be slipped inside the helices and soldered. It's easier and less likely to result in damage than trying to unsolder the old leads from the tags to which they are attached.

If the old lead stubs are too short for a helix, you can just form them into small hooks, do the same with the new cap leads, squeeze them together and solder. Not quite so neat but just as effective.

[cathoderay57]

Originally Posted by Morayfirthaudio

When I typed in the capacitor needed, there is about a dozen different shapes and sizes so I’m not keep on chucking anything in even although it’s the correct value. So I’ll need to dig a bit deep to make sure I’m getting it right. I did see a link to CPC for a capacitor but the link is dead so I’ll need to do a bit more homework

Here's a link to a suitable type of capacitor (in this case 0.01uF 400v). I have no connection with RS Components and other reputable suppliers are available! These yellow poly caps are frequently used to replace the waxies. https://uk.rs-online.com/web/p/polye...itors/1854280/ Cheers, Jerry

[HamishBoxer]

The Yellow .01uf 400 volts on Ebay are fine as well.

[David G4EBT]

A few comments which might be of interest.

Trader Sheets v Manufacturers Data:

Trader Sheets are fine for more experienced restorers, or are better than nothing when no manufacturers data exists. The Trader Sheet will generally be just 2 - 4 sheets, whereas - especially in the case of Bush - the maker's data will be far more comprehensive. For the AC11, Trader Sheet 951 is four pages, whereas the Bush data runs to 11 pages. (Sometimes it can be helpful to have both, but always refer to whichever sheet is being used as component numbers between the two will differ).
Likewise, for the ubiquitous DAC90A, Trader Sheet 1161 is just two sheets, whereas the Bush data runs to eight sheets.

Such commonplace sets are often a first set for novices to cut their teeth on, so the better the data, the more help it will be. To take the Bush AC11 - all that the Trader Sheet gives is the value and role of each capacitor. The Bush date also states the working voltage, the type (paper tubular, silver mica, moulder mica, etc), and the tolerance. Likewise, with resistors, the Bush data gives the wattage rating and tolerance - the Trader Sheet give neither.

If someone said: ‘’before you do anything else, replace the AF coupling capacitor’ (C29 on the Trader Sheet - C33 on the Bush data), the Trader Sheet simply says that its value is 0.1 uF – nothing more. The Bush data is more descriptive – if refers to it as: ‘0.1uF paper tubular capacitor, DC Working Voltage 350V, tolerance +/- 20%, coupling to V4 Control Grid'.

Silver Mica capacitors are generally reliable, as often as not are in tuned circuits, and ought not to be replaced unless a proper diagnosis with test equipment shows that they’re faulty. If replaced, it’s likely that the set will need to be re-aligned with a signal generator. Sometimes newcomers will say: ‘I’ve replaced all the capacitors’, which begs the question 'why?' Just relying on a Trader Sheet, unless a newcomer can recognise the various types and knows that silver mica ones should on the whole be left alone, but ‘mouldseal’ and waxy paper tubular capacitors will often need replacement, it’s likely that needless faults and complications will arise.

If you haven’t bought the DVD ROM, (which soon pays for itself), when you get an instant download, it costs £1.99 however many or few the pages are, so it makes more sense to download the more comprehensive Makers’ data.

Regarding winding a little ‘coil’ or helix on the end of replacement components to connect to a short piece of the original component ends – for example where a capacitor or resistor has been snipped off a solder tag on a valve base tag - that avoids disturbing the wiring on the tag, which will often have other components attached. It makes no sense to try to unsolder the old component, especially on cramped valve-holders such as B7G or B9A. Pi1 & Pic 2 below show coiled leads used to extend short tags on a capacitor.

As to polyester capacitors suitable for replacement of tubular ‘waxy’ paper capacitors, ‘dunkselectrocshop’ is a UK supplier who sells a wide range of good quality 630V ones in packs of five or ten. (I’ve no connection other than as an occasional customer). His online ‘shop’ is here:

https://www.ebay.co.uk/str/dunkselec...p2047675.l2563

Without wishing to state the obvious, don't attempt to do any soldering on valve-holder tags with the valves still in place. The valve pins will act as a heatsink, and you might inadvertently unsolder the fine wire from the valve 'bottle' in the centre of the valve pin, apart from risking damage to the glassware.

If you're going to do a full restoration on any set, it makes good sense to make a simple cradle so you can work safely, carry out live testing safely, and avoid damage to the set if it topples over on the bench.

Below in pic 3 is a simple cradle I made when restoring a Bush AC41. Just four pieces of flat steel bent and attached to the chassis then screwed to a scrap piece of plywood. If you look at the bottom left of pic 4, you'll see a polyester capacitor with coiled ends. Pic 5 shows the components that I had to replace. It would be silly to do that amount of work, and live testing, with the chassis just propped up on the bench.

Hope that helps a bit.

[Morayfirthaudio]

Guys, not too sure how to say thanks for all the advice, totally brilliant.
Herald1360 - that's it!! Sussed it now, know exactly what you mean.
Cathodray57 - that will do it nicely.
Hamishboxer - added advice always welcome
DavidG4EBT - that's brilliant!!! I'm very wary of the valve set up as I've only worked on pop out pop in panels on an old Philips G11 TV, so although I'm a dab hand with a soldering iron I'll not say I'm a dab hand with valves so I'm grateful for all the advice.
I've got very little aluminium to make a cradle but I make look to make it out off wood.
I did read on here about being very careful not to go mad and replace all the eye can see or you will run into serious problems with the Bias of the set. So I'll dip my toe in slowly.
In appreciation for all the help, I have put together a simulated BBC Broadcast from 1939. It's just for fun, but if anyone here would like a copy just pm me and I'll email it over. It's about 30meg in size, but it's a bit off fun just to show off your Radio the old fashioned way.
I'd better say that this is of course that you have an MP3 player fitted

[Morayfirthaudio]

Guys, a little bit of help if you could...
So I’ve track back the capacitor to what I think is that chocolate Briwn rectangle one which as far as I can detect should be of leg 4 on the V3 valve, so before I start cutting does that look right or have I got it totally wrong?
Thanks again

[HamishBoxer]

It goes to Pin 6 on V4 through a resistor.From Pin 2 on V3.

[ms660]

The square looking brown capacitor that's facing the camera in your photo looks like the AGC coupling capacitor (C23 on the Trader sheet) It couples the IF signal to one of the diodes which functions as the AGC diode within V3 .

The coupling capacitor for the control grid of the audio output valve (V4) is the wax capacitor that's furthest to the right in your photo (C29 on the Trader sheet)

Lawrence.

[crackle]

No that is NOT the audio coupling capacitor.
The chocolate brown one is a mica cap and can be left in place.
see attached picture, C29 is arrowed.
Mike

[Morayfirthaudio]

Guys Thank You �� Crackle. Thank you, I must be reading the Trader sheet upside Down!!
The top circuit board I'm a bit concerned as it looks a bit damp? Especially the component on the far right, not in the picture, but it looks like it's weeping! So the capacitors running along the top also look a little damp like grey are heating up. Could I be worrying over nothing?

[David G4EBT]

As I said in post 11, you'd be much better off using the Bush Service Data.

As I said in that post, the Trader Sheet simply says that audio coupling capacitor (C29) is 0.1 uF – nothing more. It doesn't tell you what type of capacitor it is, or its working Voltage. The Bush data (where it's referred to as C33) is more descriptive – if refers to it as: ‘0.1uF paper tubular capacitor, DC Working Voltage 350V, tolerance +/- 20%, coupling to V4 Control Grid'.

An experienced restorer can get by quite nicely with a Trader Sheet as they'd just look at where the capacitor is connected and what type it is by reference to the circuit, noting that it's connected to pin 2 of V3 (the anode). Often a Trader Sheet is all that's available, but better than nothing.

Likewise, the capacitor you have highlighted is a moulded mica one - not a tubular one, but the Trader Sheet makes no mention of that.

As Lawrence says, it's referred to as the 'AGC coupling capacitor.' However, on the Bush Service Data (where it is called C31) it's more fully described as the 'coupling capacitor to the AGC diode, Moulded Mica, 350 V 20% tolerance'. If you used the Bush data, you'd know that's not the audio coupling capacitor on sight, because you're looking for a tubular paper one - not moulded mica. (which are generally very reliable).

The circuit on the Trader Sheet doesn't show valve pin numbers on the valve diagrams - only alongside the circuit, and even then the pins aren't numbered. The Bush Data shows the valve pin numbers on the circuit itself, and nice clear layouts of each valve as they will appear when viewed on the underside of the chassis.

The Trader Sheet only gives component numbers so to see what the value of a capacitor or resistor is, you need to look it up in the parts list. The Bush Data shows the value of the components on the circuit diagram. For resistors, the Trader Sheet doesn't state the Wattage if any need to be replaced - the Bush Data does state the Wattages.

I don't want to appear critical - just saying that you can make life less complicated for yourself by using the Bush Data. Countless newcomers have struggled with the ubiquitous Bush DAC90A as a first restoration through relying on the 2-page Trader Sheet instead of the far more comprehensive eight-page Bush data sheet.

Whichever sheet you use (so far, only the Trader Sheet) do state which one as confusion between Trader Sheets and Maker's Data due to differing numbering of components.

Every good wish with the restoration.

[Morayfirthaudio]

Thanks David. I think it’s because I can see the advantages of the Data sheet, it’s like out of sight out of mind. Soooo... I’ll get the Data sheet, make sure it’s the right way round. You know by your description it’s going to make life easier, and by the looks of things, although it’s a nice clean set, I think I’ll need to do a little more replacing.
Really appreciate all the info, it’s a massive help

[teetoon]

Hello. I wonder if these pictures might help you. I did this one a few years ago and you can see the yellow caps I fitted as a minimum for safe operation as they are in critical positions where failure would lead to damage.
The third pic is the cap on the output transformer primary.

Ignore the large smoothing caps in the middle as they were like that when I got the chassis and have yet to see if the original cap will reform.

David.