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Old 7th May 2020, 1:52 pm   #41
DonaldStott
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Default Re: Another Bush DAC 10

As a follow up to my recent Post I've now had a chance to re-check all my voltage readings across this set.

The valve data in the Service Instructions make it clear that all measurements shown therein were taken with an input of 230V A.C. 50 cycles, the Receiver set to medium wave range with no signal and with an AVO 7 with chassis negative. All my measurements have been taken with my Toolzone DMM so some adjustments are required.

All values shown in brackets are from the Service Instructions.

Firstly, the heaters:-

V1 UCH42 13.3V (14.0V)
V2 UF41 11.1V (12.6V)
V3 UBC41 12.8V (14.0V)
V4 UL41 43.0V (45.0V)
V5 UY41 30.0V (31.0V)

Total 110.2V (116.6V)

Secondly, the valve pins:-

V1 UCH42

Pin 2 84.6V (98.0V)
Pin 3 45.3V (47.0V)
Pin 5 45.6V (47.0V)
Pin 7 0.74V (??)

V2 UF41

Pin 2 60.8V (74.0V)
Pin 5 50.1V (57.0V)
Pin 3, 4 & 7 1.04V (0.8V)

V3 UBC41

Pin 2 63.5V (74.0V)
Pin 7 1.05V (1.3V)

V4 UL41

Pin 2 192.7V (190.0V)
Pin 5 84.0V (98.0V)
Pin 3 & 7 4.38V (5.0V)

V5 UY41

Pin 2 208V A.C. (220V A.C.)
Pin 7 204V (205V)


So in general the HT is a bit low across the set but nothing looks particularly out of the ordinary or raises cause for concern??

Also checked the control grid of V2 (UF41) and measured 0.08V (?) while the control grid of V4 (UL41) measured 0.0V.

What I did find was that on some occasions when the set was switched on from cold that the volume was a lot quieter than usual and didn't mute when the volume control was turned to zero. I understand that this may be symptomatic of an ailing UBC41? I accidentally shorted the control grid (Pin 5) of the UBC41 to chassis and found that this cleared the problem?

Any and all feedback welcomed.
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Old 8th May 2020, 1:53 pm   #42
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Default Re: Another Bush DAC 10

So what I've done is to switch over a UBC41 from a known working Bush DAC90A - no change to the volume issue?

That tends to rule out the UBC41?

Checked the wiper on the volume control (VR1) with the set switched off and getting a healthy 0Ω - 486kΩ on one side and 486kΩ - 0Ω on the other so that tends to rule out a dodgy volume pot?

Tried wiggling all the valves to see if there was any crackling but nothing to indicate misaligned pins or pin sockets?

To me it sounds as if something is "floating" or not making contact with the chassis properly, but that's really my best guess?

Still not sure if any of my valve pin readings are indicative of a problem somewhere?

Any advice on where to check next ... ??
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Old 8th May 2020, 4:11 pm   #43
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Default Re: Another Bush DAC 10

What's the actual problem - 'mush' between stations? Most of the time that's down to the amount of digital noise these days, there was none when these radios were first used. I have a CFL lamp with magnifier on the bench, if I turn that on when a set is on then the noise drowns out most signals!

Your voltages seem fine - closer than on the set I recently renovated.
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Old 8th May 2020, 4:53 pm   #44
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Default Re: Another Bush DAC 10

Thanks for your response Keith.

The problems with the volume detailed in my Posts #41 and #42 above have largely been resolved.

Background mush and between station noise is an ongoing issue but as I said earlier "It's still amazing how quieter things become when all other electrical equipment in the vicinity is turned off - one of the prices we pay for our modern, connected society!" - maybe I just have to accept that it's as good as it gets?

Just as an experiment I've ordered up one of those Visaton 5" Full Range Speakers to see if alleviates any of the scratchiness/buzzing from the existing speaker as it seems impossible to disassemble this?
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Old 9th May 2020, 8:00 pm   #45
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Default Re: Another Bush DAC 10

Hopefully we are on the home straight now and headed for the finish line so our attention turns to the cabinet and associated features.

I have crack in the Bakelite case to the rear of the pre-set buttons which I have secured with superglue and some reinforcement to the rear - time to look out the wet and dry and get polishing!

As with many other parts in this set the u-shaped black strips either side of the dial glass have come to pieces and are not re-usable! Are there any suitable alternatives?

For those of you who may have been following this Thread (!) you may remember that I had to fit an additional 10W resistor to compensate for the damaged Dropper. This does mean that this area of the set can get very hot as we have the Dropper, the new 10W resistor and the Rectifier valve (V5) in close proximity to each other. I'm considering fitting some form of heat resistant/insulated sheet on the inside of the case as a precaution. What would Forum members recommend - lots of options on eBay and elsewhere but too many for me to make any sensible choice?

Thanks for any help and/or suggestions.
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Old 10th May 2020, 11:44 am   #46
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Default Re: Another Bush DAC 10

Here is a picture of the remnants of the perished u-shaped black strips that fit either side of the dial glass - very brittle:-
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Old 10th May 2020, 12:34 pm   #47
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Default Re: Another Bush DAC 10

https://www.ebay.co.uk/i/22263399035...SABEgLM8_D_BwE


Kind of thing?
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Old 10th May 2020, 1:21 pm   #48
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Default Re: Another Bush DAC 10

Exactly what I need - thanks Chris.
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Old 11th May 2020, 5:08 pm   #49
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Default Re: Another Bush DAC 10

Still experiencing problems with the scratchy/buzzy loudspeaker.

Tried some 4 BA bolts and nuts to clamp the front plate tightly to the main body of the speaker and although this improved things a little, the problems are still very audible.

The new Visaton Model FR12 speaker arrived today and that was quickly connected - what a difference in sound quality and no scratchy/buzzy noises! Looks like it might be staying connected permanently although I'll need to fashion a suitable circular surround from MDF or plywood to accommodate the smaller diameter of speaker.

Given the inquisitive nature of Forum members I am somewhat surprised that no one has attempted to disassemble one of these DAC10 Celestion speakers - well nothing that I could find after doing a Forum search?
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Old 3rd Jun 2020, 9:40 am   #50
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Default Re: Another Bush DAC 10

Finally found some time to get back on track with this DAC10.

Looking back over this Thread I noticed that there are a few questions where there was no response - hope someone can help with these: -

1. The loudspeaker is scratchy and sounds like there is "stuff" trapped in the workings or a misaligned suspension? The main magnet is an obvious source of "rust dust" and it would be good to get "in about it" to give the speaker a proper clean and check. Given the inquisitive nature of Forum members I am somewhat surprised that no one has attempted to disassemble one of these DAC10 Celestion speakers?

2. Background mush and between station noise is an ongoing issue - is there any way to get better/cleaner reception with the DAC10?

3. I had to fit an additional 10W resistor to compensate for the damaged Dropper. This does mean that this area of the set can get very hot as we have the Dropper, the new 10W resistor and the Rectifier valve (V5) in close proximity to each other. I'm considering fitting some form of heat resistant/insulated sheet on the inside of the case as a precaution. What would Forum members recommend - lots of options on eBay and elsewhere but too many for me to make any sensible choice?

4. And a more general question which strays into an area I have avoided so far - when and how do you know that a set needs realigned??
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Old 5th Jun 2020, 10:19 am   #51
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Default Re: Another Bush DAC 10

While waiting for some responses (please) to my questions in my Post above I've been finalising the outstanding tasks with this set.

I've fashioned a suitable circular surround from MDF to accommodate the smaller diameter Visaton Model FR12 speaker and that is now fitted and working well.

I've repaired the crack in the Bakelite case just to the rear of the pre-set buttons (so hardly seen) and polished everything up with Greygate No. 5 and final finish with Beeswax - nice.

A new diffuser cut from transluscent plexiglass has been fitted (thanks to Northyorks1 for the link) and this has improved the illumination from the bulbs.

While reception on MW is good, LW is not so great compared with the other sets I have in my collection. When I adjusted the pre-set buttons I have Radio 4 LW on Button 1, a very, very weak Radio 4 MW on Button 2 (that's all?) and good BBC Radio Scotland MW on Button 3. Strangely enough when I manually tune Radio 4 LW on Button 5 I get far better reception than with the pre-set on Button 1? Is there any way to improve this situation or is this as good as it's going to get?
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Last edited by DonaldStott; 5th Jun 2020 at 10:20 am. Reason: Typo
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Old 5th Jun 2020, 11:19 am   #52
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Default Re: Another Bush DAC 10

Make sure the switch contacts are making ok, if they are and the stations are weaker on preset than on manual then that would suggest that the trimmers/coils for the presets are out of alignment.

Lawrence.
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Old 5th Jun 2020, 1:28 pm   #53
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Default Re: Another Bush DAC 10

I go round the edge of the speaker between the cone and frame the magnet is attached to with a bent paperclip to get any accumulation of fluff out. I have slackened the two screws on the magnet and tapped the magnet so it's not rubbing on the voice coil/former. This can take quite a while to get right. I'm not sure if the screws hold the whole magnet assembly to the frame, or hold the pot and pole pieces together, either way I seem to have 'got away' with doing this. Usually if do this on a normal speaker it is extremely difficult to realign the pot and pole pieces.
I think I have once taken the whole front frame off, I think it is just pressed in, but you risk damaging the cone doing this as it may be stuck to the front frame in places. See what others say
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Old 6th Jun 2020, 3:26 pm   #54
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Default Re: Another Bush DAC 10

Quote:
Originally Posted by ms660 View Post
Make sure the switch contacts are making ok, if they are and the stations are weaker on preset than on manual then that would suggest that the trimmers/coils for the presets are out of alignment.
Thanks Lawrence - despite using contact cleaner twice on the switches they still look a bit mucky under the magnifying glass.

I've used Servisol Super 10 and DeoxIT Fader F5 so far and was contemplating using some liquid rosin flux on the contacts - it will be applied with a needle dropper but any dangers here??
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Old 6th Jun 2020, 3:55 pm   #55
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Default Re: Another Bush DAC 10

Here's a quick picture of the switch contacts - from the right the first two look o.k. probably as these are the MW and LW manual tuning and clearly the most used?

The next three, from the middle to the left, have seen better days and appear to have had some form of coating in certain areas?

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Some abrasive cleaning of the switch contacts would be the optimal solution but don't want to risk damaging any of the delicate components here!
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Old 6th Jun 2020, 4:21 pm   #56
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Default Re: Another Bush DAC 10

Quote:
Originally Posted by DonaldStott View Post
Quote:
Originally Posted by ms660 View Post
Make sure the switch contacts are making ok, if they are and the stations are weaker on preset than on manual then that would suggest that the trimmers/coils for the presets are out of alignment.
Thanks Lawrence - despite using contact cleaner twice on the switches they still look a bit mucky under the magnifying glass.

I've used Servisol Super 10 and DeoxIT Fader F5 so far and was contemplating using some liquid rosin flux on the contacts - it will be applied with a needle dropper but any dangers here??
I can't comment on the flux because I've never used it for switch contacts, only ever used spray contact cleaner or back in the old days carbon tet.

Lawrence.
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Old 6th Jun 2020, 7:21 pm   #57
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Default Re: Another Bush DAC 10

All switch contacts cleaned once again with Servisol Super 10 and things are better but this made no difference to reception on Push Button No.2, one of the MW Pre-sets.

The Push Button Ranges on my set differ from what is listed in both the Bush Radio Service Instructions and the Bush DAC10 Trader Service Sheet 1002 - all just to confuse someone like me!

What I have is: -

Push Button No.1 - 1200-2000 Metres
Push Button No.2 - 550-350 Metres
Push Button No.3 - 350-200 Metres
Push Button No.4 - LW Manual Tuning
Push Button No.5 - MW Manual Tuning

I've adjusted the projecting (oscillator) and recessed (aerial) screws to give me the following pre-sets: -

Push Button 1 - BBC Radio 4 LW (1500 Metres)
Push Button 3 - Clyde 2 MW (261 Metres)

I was hoping to get BBC Radio Scotland MW on Push Button 2 (370 Metres 810 kHz) but can't really get anything at all with this pre-set - just some very faint signals and lot of noise?

I don't want to start "twiddling" anything else as these pre-sets are adequate as is the LW and MW manual tuning.

Not sure where to go looking to fix the issue I have with Push Button 2 and no signals. BBC Radio Scotland MW should fall within the range covered by this Push Button.

My Heathkit Signal Generator is out of action currently awaiting some TLC!
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Old 6th Jun 2020, 8:46 pm   #58
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Default Re: Another Bush DAC 10

If you reverse the push button numbers you've given it's the same as the Trader sheet, if the contacts are ok it might be worth checking the coil.

As an extra note, Bush modified button number 2 (Bush numbering) for LW preset (shown at the end of the Bush manual) Then later it was moved to button number 1 (Bush numbering) which is button number 5 in the Trader sheet:

https://www.vintage-radio.net/forum/...6&d=1518265749

Lawrence.

Last edited by ms660; 6th Jun 2020 at 9:02 pm. Reason: Extra info
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Old 6th Jun 2020, 8:58 pm   #59
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Default Re: Another Bush DAC 10

Quote:
Originally Posted by ms660 View Post
If you reverse the push button numbers you've given it's the same as the Trader sheet...
As I said, all just to confuse someone like me!

Quote:
Originally Posted by ms660 View Post
... if the contacts are ok it might be worth checking the coil.
Looking at the Bush DAC10 Trader Service Sheet 1002 I think it shows that coil L4 is associated with Push Button No.2 in my numbering system.

Click image for larger version

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And in the Bush Radio Service Instructions this is shown as coil L2.

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At least both these sources agree that the coil in question has a resistance of 2.0 ohms. Is there anything else I can check here??

Quote:
Originally Posted by ms660 View Post
As an extra note, Bush modified button number 2 (Bush numbering) for LW preset (shown at the end of the Bush manual)
Noted, but my set clearly shows that Push Button No.2 covers the range 550-350 Metres - so MW??
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Old 6th Jun 2020, 9:09 pm   #60
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Default Re: Another Bush DAC 10

Check the coil.

Lawrence.
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