Bush DAC90A FM Conversion

[bobhowe]

Hi ordered the David Winter FM board for tube radios & while I am waiting for for it to arrive I am preparing this DAC90A chassis for my ivory set . 1st thing I have done is give it blanket change and stuff the waxie capacitors replace with a NOS volume pot / switch & as recommended class x2 10nf suppression capacitor across the switch .Old wiring has been changed next step is to change the mains dropper to the Ed Dinning auto transformer hear is some pictures more to follow

[FERNSEH]

Hi Bob,
in order that a three position waveband switch can be fitted in a DAC90A, modifications to the switch bracket are called for.
A very small four-pole three-way switch measuring only 28mm diameter can be fitted in the extra space made for it. See attachments.

DFWB.

[Radio tirana]

Hi Bob, looking forward to hearing how you get on with this project, I have also ordered a module to try not sure what I am going to use as a test bed yet.

Kind regards RT

[agardiner]

I am also looking forward to hearing how you get on, having ordered some of David's modules.

I have previously converted a few DAC90A sets - some to FM and one to DAB, using the also excellent modules from HSE. Plenty of owners have DAC90 sets, and love the idea of being able to listen to their everyday stations on them!

[bobhowe]

Hi David adaptor plates here we go . Hi RT the audio amp stage on this DAC90A there is no noise so the sound quality on FM is going to be very good will report findings as it happens

[bobhowe]

Originally Posted by agardiner

I am also looking forward to hearing how you get on, having ordered some of David's modules.

I have previously converted a few DAC90A sets - some to FM and one to DAB, using the also excellent modules from HSE. Plenty of owners have DAC90 sets, and love the idea of being able to listen to their everyday stations on them!

Hi did your conversion use the original valves and tuning capacitor

[agardiner]

Originally Posted by bobhowe

Hi did your conversion use the original valves and tuning capacitor

Yes. The HSE adapter replaces only the mixer valve (UCH42 in the DAC90A), so obviously you lose the AM bands. It receives the FM signal, tuning with the original capacitor and then re-modulates the signal onto an AM IF carrier, so the remainder of the set is still used.

I really like the look of David's modules, but think there is also a place for the HSE ones. Easier to integrate the HSE module particularly in a live chassis and series heater chain, as you don't need to consider power. That said, they have to be built for the particular set and obviously cost a lot more.

Each set/customer is different, so it is great to have both solutions available. I think the demand for FM and indeed DAB conversions will only increase with time.

[bobhowe]

Originally Posted by agardiner

Yes. The HSE adapter replaces only the mixer valve (UCH42 in the DAC90A), so obviously you lose the AM bands. It receives the FM signal, tuning with the original capacitor and then re-modulates the signal onto an AM IF carrier, so the remainder of the set is still used.

I really like the look of David's modules, but think there is also a place for the HSE ones. Easier to integrate the HSE module particularly in a live chassis and series heater chain, as you don't need to consider power. That said, they have to be built for the particular set and obviously cost a lot more.

Each set/customer is different, so it is great to have both solutions available. I think the demand for FM and indeed DAB conversions will only increase with time.

Glad that there is now options to keep radios that can work on the way that were made and not ruined by the smart speaker & Squirrel cage light bulb muppets

[rambo1152]

Originally Posted by FERNSEH

Hi Bob,
in order that a three position waveband switch can be fitted in a DAC90A, modifications to the switch bracket are called for.
A very small four-pole three-way switch measuring only 28mm diameter can be fitted in the extra space made for it. See attachments.

DFWB.

Originally Posted by bobhowe

Hi David adaptor plates here we go . Hi RT the audio amp stage on this DAC90A there is no noise so the sound quality on FM is going to be very good will report findings as it happens

Switching the audio is the easy part. If you want to retain MW/LW (otherwise you wouldn't need a 3 pole switch) you will need to switch the variable capacitor between the module and the set which might not be as straight forward as it seems.

Here's a rare frontal view of the DAC90A



How about mounting an extra 500pF VC for exclusive use of the module, to a shaft coupler stuck (somehow) to the shaft?

But to be honest I think there is a different simpler approach that needs to be considered.

Why not couple a potentiometer to the tuning gang and use an FM receiver with varactor / varicap diode tuning of the sort that were common 30 or 40 years ago. What does the team think?

[vinrads]

I was thinking along the same lines but using a single 500pf tuning capacitor, driven from the dial cord , I guess only certain sets would would be viable, Mick.

[bobhowe]

NEWS-FLASH looks what has arrived from France ( Very quick postage ) thanks David Waiting for a anti static wrist band to arrive from the UK that is taking longer before I start to work on it

[agardiner]

Awesome.

[agardiner]

How about mounting an extra 500pF VC for exclusive use of the module, to a shaft coupler stuck (somehow) to the shaft?

But to be honest I think there is a different simpler approach that needs to be considered.

Why not couple a potentiometer to the tuning gang and use an FM receiver with varactor / varicap diode tuning of the sort that were common 30 or 40 years ago. What does the team think?

Yes, I think that is a good idea, although it obviously depends on the set and the space to achieve it. There is no doubt that each set needs its 'own' approach and there is no 'one size fits all' solution. What matters most is being able to do it and keep the set alive and in use.

[bobhowe]

UPDATE could not wait for the anti static strap to arrive bought a anti static mat and followed Davids instructions temporary wired the board on the antistatic calibrated it and a great result board works fine. Two points to consider 1. as David says the tuning gang has to be perfect and the other is the radio being a DAC90A ( not the board ) needs some work on the audio stages. I am very pleased with this board and how easy it is to set up. I'm going to order another board as this is going to be FM only. Here are some pictures, more to follow when the board is installed.

Kind regards, Bob

[Radio tirana]

Hi Bob well done Great to hear that the board worked straight away, I thought it would be hard to resist wiring it up. I am thinking of fitting this module to my Philips 462A it has a large speaker and great sound when fed from the gram input or a Minimod.
I will follow your progress and will post some pictures when my module is wired up and tested

Kind regards RT

[bobhowe]

Hi RT as David Winter says in his instructions the board should be well grounded and the tuning capacitor must have no faults one thing I am going to do is install the board close to the tuning capacitor so there is no long wire run . it will sound really great in your Phillips 462A

[FERNSEH]

With modification to the bracket the 4 pole 3 way Lorlin switch will fit in the space between the control shaft and the and the wavechange switch.
But more clearance is needed to avoid the tags on the new switch coming into contact with the tuning control shaft.

DFWB.

[david winter]

Originally Posted by bobhowe

Hi RT as David Winter says in his instructions the board should be well grounded and the tuning capacitor must have no faults one thing I am going to do is install the board close to the tuning capacitor so there is no long wire run . it will sound really great in your Phillips 462A

The board should be grounded first. You don't have to solder all corners. I gounded three corners to make it easier. My previous version of the board didn't have the holes, so I had to solder from the bottom. In most cases, two strips of "disoldering wire" made strong joints. The holes make it easier to solder, and eventually screw as well (I used 2.6mm holes so that both 2.5mm and 2.54mm screws pass without trounble).

I've done a number of radios with a "long" wire between the tuning capacitor and the board (maximum 10 inches). Never a problem, but I awlays place the board as close as I can from the tuning capacitor. If the wire has to be that long, I make sure it is hard enough to stay free. And even if you have to make the wire pass here or there, the added capacitance won't hurt as the calibration steps will take this into account automatically.

However, use a shielded audio wire (I personally ground it using the electrolytic capacitor's negative pad, which makes it easier to connect only one hot point to the amplifier's input. The only cases where I used a single, non shielded wire was when the board was close enough to the amplifier's input or from a shielded wire going to it (i.e maximum 2 inches).

I once had too much residual hum on a radio and used a 3-wire mains cord with chassis to the earch, thus removing those capacitors between the mains and chassis (and adding one over the mains switch). As a result, the radio was absolutely NO residual hum. However, I think I once had another case of "earthed chassis" where I had no hum only if the phase arrived to one specific edge of the mains transformer.

By the way, it would be interesting for everybody following this thread that you add a video of your radio working.

[FERNSEH]

The bracket has been repositioned again to make more space for the switch tags.

DFWB.

[bobhowe]

Originally Posted by FERNSEH

The bracket has been repositioned again to make more space for the switch tags.

DFWB.

Hi David glad you have managed to fit the switch in the limited space