Bush radio. BA91

Without seeing a photo of your set, from your description and valves I would say its a BA91. This was the battery version of the DAC90/90A. The service manual for the BA91 is in the data library. ? 

A picture would be nice ? 

Looking forward to reading more about it, sounds an interesting set.

Always something new to learn, I had not heard of theses valves before. Introduced in 1946 while the 1.4v Dxxx range was 1947, can’t be many radios with the K series valves around

I didn't bother with a picture seeing as it looks just like a DAC90. Thanks Chris. A BA91 seems logical. Maybe Cathovisor can fill in some details sometime.

Here is the original listing https://www.ebay.co.uk/itm/Bush-Bakelite-AC91Valve-BATTERY-Radio-Quite-Rare-Spares-or-Repair-Good-Case-/323909919786?_trksid=p2047675.l2557&nma=true&si=MdM%252Fb5iim2OndgY8bPVK5ypmuJ4%253D&orig_cvip=true&nordt=true&rt=nc

The K series don't seem very plentiful either. The rarest one seems to be the KCF30.

The picture in the listing shows the KCF30 appears to have been subbed....it's mounted onto another base. I wonder if the set has been modified? The original valve is shown as a triode-hexode despite having an 'F' (pentode) designation. I don't think there were many triode-hexode battery valves made but possibly Mazda did some.

Just noticed it has a shortwave band!

Valve data for :-

• V1 KCF 30
• V2 KF 35
• V3 KBC 32
• V4 KL 35

Interesting that it's shown as a pentode in that data in keeping with it's 'F' designation but drawn as a hexode in the Bush circuit. The National Valve Museum don't show a description although it is listed.

BA91. Absolutely no shadow of a doubt. ? 

I've got one: beware the usual detached iron-dust cores in the IF transformers! I restored mine many, many years ago and was impressed by the silent background that comes from battery operation. In particular, I remember listening to a classical music concert from Deutschlandfunk on MW in the dark in the front room at low volume, whilst Anne slept on the sofa...

Some of the sets had overprinted backs; one of my sets says 'EAC91' under the printed 'AC91' - the EAC91 being the export version. Bush did market a small plinth for the set to sit on that housed the HT battery, but I've never seen one. That chassis had a final fling in the BA11 wooden table set but by then it had gained Mazda valves as I think Mazda were the last manufacturers of 2V octals.

The adaptor looks like it's been made to take a Mazda TP25 in place of the KCF30.

To be honest, a bit of me thinks that KCF30s were actually TP25s in disguise.

Posted by: @cathovisor

BA91. Absolutely no shadow of a doubt. ? 

and was impressed by the silent background that comes from battery operation.

Hi Mike. So how do you power yours....HT is relatively easy but what about the two volt filaments?

How about one of these

The Bush BA91 service manual shows the KCF30 as a triode-hexode but it is really just a re-based Mazda TP25 triode pentode.  Some KBC32 double-diode-triodes are rebased Mazda HL23DDs.  Output valve is a Mullard KL35 pentode.  Pye made a battery version of the popular mains powered model 15A. The model 65A went one better over the Bush BA91 by employing a QP25 double-pentode output valve.  The made in Ireland version is the model 69A.

Till Eulenspiegel.

Posted by: @sideband

Posted by: @cathovisor

BA91. Absolutely no shadow of a doubt. ? 

and was impressed by the silent background that comes from battery operation.

Hi Mike. So how do you power yours....HT is relatively easy but what about the two volt filaments?

Well... many years ago, "Dinosaur" Dave Grant designed a rather neat little power supply that used some transformers that came from the Purley Way clearout. With a DPDT plus centre-off switch we had 1.4+90, 2+90 and 2+120 volt supplies and that's how I power mine. Unfortunately not all Bush battery sets were that easy to power; for some years both pre- and post-war they used 72V and 144V HT supplies.

An LM317 regulator will give a clean, noise-free supply for the valve filaments (the 317 works down to 1.25V); or you can use Chris's suggestion of one of those lovely 'Cyclon' cells which are perfect for the job.

Posted by: @till

The model 65A went one better over the Bush BA91 by employing a QP25 double-pentode output valve.  The made in Ireland version is the model 69A.

There is an Irish/export version of the BA91 that uses the same valves as the 65/69A.

Posted by: @cathovisor

 

An LM317 regulator will give a clean, noise-free supply for the valve filaments (the 317 works down to 1.25V); or you can use Chris's suggestion of one of those lovely 'Cyclon' cells which are perfect for the job.

Well the rechargeable cell is certainly food for thought...presumably there is a suitable charger available as well.

The use of the LM317 is also interesting....I have a small power supply that delivers 90V and 1.5V...the 1.5V uses an LM317 so I only need to alter the fixed resistor that controls the output voltage or sit the LM317 on a diode to increase the output by 0.6 volts and increase the size of the heatsink............Hmmmm! finding an extra 30 volts from the exisisting 90V shouldn't be too challenging....another little job for the dark nights!

Just add a resistor in the 317's feedback network to get the 2V Rich, it's better than the diode and you can simply short it out to return it to 1.5V.

There's also this very handy little device from Texas, the TL783. 1.25 to 125V at 750mA. Ideal for a variable-voltage HT regulator, I'd say.

There is at least one pre-war Bush table battery radio set upstairs.  The sets employ the large 7 pin 2volt valves. FC2A VP2B etc.

I will introduce these sets in a new topic.

Till Eulenspiegel.

Posted by: @cathovisor

Just add a resistor in the 317's feedback network to get the 2V Rich, it's better than the diode and you can simply short it out to return it to 1.5V.

There's also this very handy little device from Texas, the TL783. 1.25 to 125V at 750mA. Ideal for a variable-voltage HT regulator, I'd say.

That TL783 looks very interesting.....I might get one of those and have a play. Much simpler than my present power supply...

Is it just me that finds it bizarre to produce a radio in a smart, good looking cabinet and then have the batteries - including originally no doubt a wet Leclanché 2V cell - dangling around outside?