Bush AC11 - Newbie Project
 

I have just taken ownership of my mum and dad's Bush AC11 valve radio -see photo. I am so pleased as I have always loved this and played with it endlessly as a small child. The set got replaced by a 'modern' transistor radio back in the 70s and the AC11 got relegated to the garage where it got used regularly until a few years ago when my dad was no longer fit enough to do DIY. The set is a bit rough and ready but is completely original - untouched - they bought it new in 1951 and it always worked. If it started to go a little fuzzy my mum would take the back off leave it in the driveway for the wind to blow out the cobwebs and it would be right as rain again.

So, being bold I cleaned the set up inside (see photo) and out switched it on hoping for the best, apparently it worked last time dad used it. After a minute or so I managed to get radio 1 (somewhat disappointingly). A minute later nothing, it just hummed. Having started to do some research around this site I realise this may have been a bit too bold but what is done is done. I'm aware these sets are not worth a lot but this is of huge sentimental value to me and I'm keen to get it working again so it can justify the space it is going to occupy.

Me? Well I'm no stranger to oscilloscopes and soldering irons but I haven't worked with valves for several decades and even then I didn't really know what I was doing. I more used to 8V max for space qualified electronics! So really I'm a complete newbie for this project. This is also my first post so please excuse my lack of knowledge.

I've looked around the site and have spotted the following two useful threads on Bush AC11s and will be digesting what they say:
1: https://www.vintage-radio.net/forum/...ad.php?t=10946
2: https://www.vintage-radio.net/forum/...d.php?t=158637

I've also got the Trader sheet 951 on the set and intend to purchase on-line the Bush version - advice welcome on that - as somebody mentioned a DVD worth getting ?

From what I read wax capacitors are a main cause of failure in old radio sets and I can believe that. I think my starting position may be to replace all the wax capacitors for the modern equivalents as described in this very useful link (http://www.vintage-radio.com/repair-...apacitors.html). Again, my valve knowledge is little and I'm very wary of probing around on a live set with high voltages so any advice on the way forward would be appreciated.

Re: Bush AC11 - Newbie Project
 

I can feel the queue of members behind me, but I'm happy to report it was unlikely to have been BBC Radio 1.

Re: Bush AC11 - Newbie Project
 

Yes, no R1 on MW or LW.

This is a good beginner's set.

You may indeed need to change some capacitors, but the first thing to do is to study the circuit diagram and work out what all the components are and what they do. Then compare the diagram to the actual radio underneath the chassis. The next stage would normally be to clean all the switch contacts with Servisol 10 contact cleaner, and then measure the voltages present at the test points indicated in the service data.

If you do start to change capacitors, do them one at a time checking each time. It's easy to introduce faults.

Re: Bush AC11 - Newbie Project
 

I recently recapped one that had been in my attic for many years and now use it connected to my Amazon Alexa for music through a small Chinese amp off eBay to the gram input.

I personally replaced all of the wax capacitors on the board underneath with the correctly rated modern equivalents and also replaced the 2 core flex with a 3 core flex and earthed the chassis so the house rcdd will kick in if anything goes awry.

Hope you enjoy the project

Nigel

Re: Bush AC11 - Newbie Project
 

Before switching on again I would replace C29 (Trader sheet) with a modern 10nF 400v capacitor. If it goes leaky it puts the UL41 output valve and the output transformer at risk.

While you are in there check if any electorate has escaped from the main smoothing block C33

Re: Bush AC11 - Newbie Project
 

One little tip if I may, take some photos of the chassis, if you do change some components you may find them very handy to refer to.
Cheers
John

Re: Bush AC11 - Newbie Project
 

I see it has BBC radio dial stickers from the 1970s, you may want to leave these in place as part of the radio's history.
https://vintage-radio.net/forum/showthread.php?t=135087

If you got a station where the Radio 1 sticker is, the station is likely to be Absolute Radio on 1215kHz or 247metres.

Re: Bush AC11 - Newbie Project
 

Like a few other sets of this era, it uses series heater-chained valves connected to a high voltage secondary winding of the mains transformer, one end of which is connected to chassis. It did provide the makers an option to offer the AC/DC version of the same set sans transformer but using exactly the same valves and a mains dropper resistor. However, unlike the AC/DC variant the AC-only set will continue to work with blown scale lamps because they are powered from a separate part of the heater secondary winding. The other thing that strikes me is it is a vast cabinet in comparison to what's inside it! Cheers, Jerry. Oops, silly me, just spotted R28 that bypasses the scale lamps on the AC/DC variant :dunce:

Re: Bush AC11 - Newbie Project
 

Thanks for all the replies, much appreciated.
Somewhat embarraassed about the Radio 1 thing :-[ I'm sure it was there last time I used that radio...
I'm going to read through the service sheet a few time to get my bearings & I'm trying to do a bit of background learning on valves.
I'm going to pull the chassis out of the box so I can start to work on it. I will take lots of photos to help me. I've got some servisol so I can clean up the switches and pots. I'll replace " replace C29 (Trader sheet) with a modern 10nF 400v" and check C33. Any other obvious ones to replace or it that a good starting position?
Yes it does have those little stickers - I remember all that happening at the time - so definiatley part of that sets history.
Is there a good bit of text to read on safety aspects of working on these high voltage sets? Don't want to make aany sillt mistakes.8-o
Anyway - thanks again

Re: Bush AC11 - Newbie Project
 

I recommend you follow the excellent guidance here https://www.vintage-radio.com/repair...and-tests.html Cheers, Jerry

Re: Bush AC11 - Newbie Project
 

These are not particularly dangerous to work on, though there are high voltages present which can give you an extremely unpleasant belt. You shouldn't touch anything potentially live with your fingers or an uninsulated tool with power applied unless you are absolutely certain you know what you're doing. You should also make sure that your body isn't earthed, e.g. you're not resting your body on a central heating radiator. An old repairman's dodge is always to work with one hand in your pocket. This means that any shock won't be across your chest and so is highly unlikely to be fatal.

C29 is the only 'must change' component. If leaky (and it will be), it will cause the UL41 output valve to overrun, damaging both it and the output transformer. Replacement UL41s are pricey.

Re: Bush AC11 - Newbie Project
 

Thanks again for your comments. I'm going to read and follow the advice in "Initial Checks and Tests". I'll get caps ordered so I can change C29.

In the meantime I have found a bit of time to pull the chassis out, and it was really easy. It's all completely original - never repaired and most of it looks in good condition to me. No leakage from mains smoothing C33. The only worry I can see is a darkening of the main transformer. I will test resistances on main & audio transformers and compare to Trader sheet. There are some new pics attached.

Re: Bush AC11 - Newbie Project
 

Remember when you remove the chassis you will have to disconnect the frame aerial and output transformer. When I work on similar sets i use an external frame aerial ( very easy to make ) and a made up lead for output transformer.
Cheers
John

Re: Bush AC11 - Newbie Project
 

Replacement caps ordered.

Re: Bush AC11 - Newbie Project
 

The chassis looks in very good condition compared to some I’ve seen.
Cheers
John

Re: Bush AC11 - Newbie Project
 

The caps arrived and I've started to go through some basic checks.

Resistance from Live to chassis is open circuit (Good)
Resistance between primary and secondary on mains transformer is also open circuit (good)
Primary side resistance are a little higher than both bush and trader but within <10% error.

Secondary side is causing me a few issues however. At first I thought it was toast (and the transformer does look a little tired) however comparing the trader sheet to the Bush sheet I can't make sense of the readings. Basically they don't agree IF I have understood them, correctly. I'm 87% of the resistance the trader sheet says and WAY off the Bush one - around 50%.

I'm going to try and summaries these and post later, but, I wondered if anybody else had come across the same problem (or is it just me).

Re: Bush AC11 - Newbie Project
 

If I understand correctly, you are measuring the secondary resistance of the Mains transformer, if this is the case the valve heaters are connected ( the dial lamps are disconnected when you remove chassis). Remove one valve and measure again you should find it closer to what you expect. I hope I haven’t misunderstood you.
Cheers
John

Re: Bush AC11 - Newbie Project
 

Visually the mains transformer looks OK - I've seen a lot worse! Usually if the transformer has had a very hard time or has winding shorts there is evidence of leaked melted wax and I can't see any on yours. You're sensible to do dc resistance checks but don't get too hung up over it; providing the HT winding isn't open circuit I would be inclined to disconnect the rectifier cathode from the HT reservoir capacitor then power it up and measure the dc voltage at the rectifier cathode. So long as it is somewhere in the order of 180-200 volts and there is no smoke or bubbling wax from the transformer then all should be well. Once you connect a replacement reservoir cap the HT voltage at the cathode should rise to the value quoted in the service sheets. If you are still using the original HT cap and the set still hums with the volume control at zero then the HT cap is almost certainly unserviceable and will need to be replaced. Cheers, Jerry

Re: Bush AC11 - Newbie Project
 

Thanks - That does help a bit.
I still think that the Bush service sheet data is incorrect!
I've attached my readings relating to both Bush and Trader service sheets.
Think I'm happy enough to carry on.

Re: Bush AC11 - Newbie Project
 

Thanks.
Added some transformer close-ups as it was easy to do with it on the bench now...