More BUSH DAC10 Woes!

[DonaldStott]

Originally Posted by astral highway

If you haven't already found this, there's an excellent write-up on relevant theory-meets-practice here...https://www.vintage-radio.com/repair...rf-stages.html Can I invite you to take a look and you'll be able to find the AGC line on your set pretty easily. Sounds like a bit of sleuthing is right up your street!

Thanks Al - of course I've read and re-read Paul Stenning's excellent articles many times over but there's nothing like having an actual problem in a set on the workbench to help focus the mind. You are correct of course as the sleuthing was indeed right up my street!

I think I've found the AGC (AVC) line in the DAC10 and, as a first step, have made sure that all associated caps and resistors are within tolerance. I'll do some voltage measuring tonight and report back. Hopefully I've properly identified where to measure the AGC voltage but no doubt I'll find out when my assignment is marked!

Originally Posted by murphyv310

There is one line of defence we have and that is the magnetic loop antenna, they massively help reduce interference.

...

My long wave reception is good here with the loop and a proper mains filter prior to the radio I'm listening to. Bring any AC/DC set indoors and forget it, it's totally useless.

Thanks Trevor - unfortunately the Bush DAC10 has no provision for an external aerial of any type. It has an inbuilt Frame Aerial with MW and LW windings.

The main reason I am persevering with the LW noise issue is that I have no such issues with any other sets in the same room e.g. Bush DAC90A, Bush AC91, KB MR10.

[murphyv310]

Hi Donald.
Yes I realise there is no provision for an external aerial on the DAC10, done a good few over the years. What I've done in the past though is to wind a simple two or three turn loop on a frame and mount it next to the existing frame aerial and is inductively coupled. This works beautifully and is fully isolated from the mains, the much better signal gives AGC action and interference etc is at a minimum.

[DonaldStott]

Looks like that I just need to accept that curing the LW background crackle on this Bush DAC10 is a bit like trying to fix the hum on a Dansette i.e. am I just chasing unicorns!

Given the slow but steady decline of AM broadcasting I'm looking at the feasibility of augmenting (not replacing) my Bush DAC10 with Bluetooth using the KRC-86B V4.0 board. I posted here but got no responses:-

https://www.vintage-radio.net/forum/...4&postcount=13

I appreciate that this may not be a suitable topic to discuss in detail on a Public Forum due to the obvious safety issues and differing levels of skills and abilities. If anyone would like to help take this forward off-Forum then please PM me - I'm hoping that such a request is within the Rules?

[murphyv310]

Hi Donald.
Why not buy or make a pantry transmitter and feed it with something of your choice.
I've made a few over the years, valve, transistor and Russian Rod pentode, the latter can be extremely simple, run on batteries and work very well indeed.

Here is a video to one I made with a 1J42A (the commentary is wrong with the valve type)
https://youtu.be/v1D0D8qTHjs

[DonaldStott]

Originally Posted by murphyv310

Why not buy or make a pantry transmitter and feed it with something of your choice. I've made a few over the years, valve, transistor and Russian Rod pentode, the latter can be extremely simple, run on batteries and work very well indeed.

I've discussed this with the person I restored the DAC10 for and he has indicated that he doesn't want yet another piece of kit that has to sit next to the radio. A pantry transmitter would be battery powered so yet another thing for him to keep an eye (or ear) on! He is much younger than me and loves his restored DAC10 but just wants the ability to use his phone to play his tunes through it!

The preference seems to be for an internally powered Bluetooth KRC-86B V4.0 board, notwithstanding the issues associated with this approach in an AC/DC set such as the Bush DAC10.

I agree that fabricating a pantry transmitter is much the easier option but anything that keeps vintage valve radios working into the future and out of the skip must be a good thing?

[murphyv310]

Hi Donald.
A pantry transmitter could be mounted inside the set and it can be isolated from mains and switchable from the DAC10 on off switch. Whether there is sufficient room though I really don't remember how crammed in it would be plus the ventilation issue you'd have with any additional electronics.

[murphyv310]

The isolation with the Bluetooth board could be an issue. Optocouplers work as do 1 to 1 audio isolation transformers, I'm not familiar with the board, I'll get a look I think and look at the feasibility.

Sorry it's Bluetooth so no isolation issues.
At that price I think I'll order one myself and have a play with it.

[murphyv310]

Hi Donald.
I've had a look at the boards and orderd one online, should be here on Monday.
I'd not use the heaters for supply as even after rectification and smoothing there will be hum or potential differences as the heaters are tied to chassis. You'd need a separate supply, even a scavenged wall wart re boxed would do. The issue might be insufficient audio drive.
Ill have a play with the one I get and report back if that helps

[DonaldStott]

I've ordered a couple of KRC-86B V4.0 modules so intending to have lots of fun with my breadboard and connecting wires!

I've constructed a 5V DC regulated power supply before but that was using a 9V DC battery input. Seems like I need to find a small enough 9V transformer and add the appropriate rectification and smoothing. Considered re-purposing a wall wart but just for prototyping.

Again not really too much of a challenge, just need a recommendation or two for the transformer. Lots of options available from overseas vendors, but which ones are safe and reliable, or do I pay more and use a 'trusted' UK seller?

[DonaldStott]

Originally Posted by DonaldStott

... just need a recommendation or two for the transformer. Lots of options available from overseas vendors, but which ones are safe and reliable, or do I pay more and use a 'trusted' UK seller?

Would this one do the business: -

https://uk.rs-online.com/web/p/pcb-t...rmers/1213822/

Secondary Voltage Rating 2 x 9V ac
Power Rating 1.5VA
Primary Voltage Rating 230V ac

[murphyv310]

Hi.
Yes I the transformer is ideal as far as I can see. Just a simple rectifier, smoothing and a 7805 regulator is all you'll need.
I received my little board from Amazon this morning and its really good, very good range, audio quality first class with no noise between tracks, also bags of output.
It's tiny in size and small in current consumption, less than 100ma so even the 7805 should run cool with no heat sink.

[murphyv310]

An update on this.
I tried this in a Pye radio that was recently saved from being used for spares. The module has loop through when the power is removed. This is the major issue. On loop through its awfully distorted, not use able. On Bluetooth play its quite good but quite toopy on the Pye, excellent on my NAD amp though. Its obviously low impedance so the Pye tone control has little effect.
It's OK ish but not a complete answer if you want to use MW and Bluetooth.

[DonaldStott]

Thanks Trevor - For the 'technically challenged' among us can you explain "The module has loop through when the power is removed."

[murphyv310]

No problem.
You can still use the radio as is. When fitting this module you need to break into the feed to the volume control so the module can feed the Bluetooth audio to the radios audio amplifier. This would be from the detector to the volume control. We then need to reconnect the detected audio back to the volume control somehow to allow the set to still work as a radio if needed. So the module has an input that we use for the detected audio. When the module is powered it disconnects the input from the detected audio and switches to Bluetooth. When we remove power to the module the audio is routed from its input to its output that goes back to the radio volume control, its called loop through. Its basically an electronic switch.

[DonaldStott]

Thanks Trevor - I think I understood most of what you explained although my challenge is how to translate your helpful words into practical steps.

If I am to use a small 9V AC transformer to supply the Bluetooth board with a rectified, smoothed and regulated 5V DC this would have to be connected to the mains supply at the radio's on/off switch. Does this mean that when the set is ON then the Bluetooth board is always ON as well?

You mentioned that " ... the module has an input that we use for the detected audio" - put simply, how do we use that?