Another day, another 'scope and more..

[djrm]

We took a detour on our way home today and visited Lincoln, on the way to the cathedral we walked past Birkett's electronic surplus shop (this want an accident). I knew Mr Birkett had died last year and it was a place I had always meant to visit, I'd seen his stalls at radio rallies and the like many times. Fortunately his daughter is continuing to run the shop and I want disappointed with what I found there. Most of the shop is filled with vintage aviation instruments and other old electronics treasure.

   


I still need to checkout the things I bought there but I think I was quite lucky to find a 400 Hz inverter, some synchro resolvers,  and 400 Hz vibrating reed frequency meter as well as a vintage switch like the one I need to replace on some old equipment.

   

When visiting the cathedral we saw a stained glass window in memory ff George Boole the inventor of boolean logic , he lived in Lincoln. 

   

Later in the afternoon we dropped in at an 'antique' shop where I found a simple oscilloscope for sale, it looks like a DIY or kit build for educational use, it is very simple. I was surprised to see it uses an 555 ic for its timebase. I can't make out the tube type just yet since the neck is wrapped in foil. it seems to be working anyway which is a bonus. I had seen it for sale previously but didn't buy it, this time I did as I thought it would be useful as a dedicated component curve tester, like this one I have been looking at recently: http://techlib.com/electronics/curvetrace.html 

   

A good day out in my books. David.

[Murphyv310]

Hi
The inverter is interesting as I was asked to repair one recently with no success, it's for an artificial horizon out of an aeroplane. I believe it's 400 hz and AC outputs.

[ppppenguin]

Is the inverter only for use on the ground (where 400Hz power isn't otherwise available) or is it also needed in the air (where standard aircraft power is 400Hz)?

[BusyBee]

It's good to hear that Birkett's is still open.It's not often I get that way although I am planning to go into Lincoln in the near future. Hopefully I will get the day right for when the shop is open.

TRacy

[djrm]

Hi
The inverter is interesting as I was asked to repair one recently with no success, it's for an artificial horizon out of an aeroplane. I believe it's 400 hz and AC outputs.

Is the inverter only for use on the ground (where 400Hz power isn't otherwise available)  or is it also needed in the air (where standard aircraft power is 400Hz)?

Hi, Judging from another Ferranti inverter I have I'd say these are backup inverters for use when the main AC power is missing. There is a master relay to enable the output, possibly overload protection. There are also three other relays which are controlled by a single DC input which will switch over some of the AC when energised - I'm not sure how this operated yet. I have verified that the no-load output is 122 V 408 Hz where 1/2 an amp is drawn from the 26 VDC  input. I'm drawing up the output the wiring first though. The unit is very nicely made for servicing and can be operated out of its casing.

   

There are three TO3 transistors, four TO5 transistors, five transformers, three large capacitors, four relays,  and a preset resistor inside. Most of the multiple way connector terminals are connected to the relay contacts, two have AC present on them when power is applied. Here is a picture of the new frequency meter being driven from the output.

   

David.

[Ed_Dinning]

Hi David, sounds like a grand day out ! Birketts also was a good source of a/c stuff

Ferranti and others made standby inverters to work off the 28vDC supply, it may even have been a standard design. Useful bits of kit for all sorts of synchro applications

Scope looks interesting, it could be a WW design from the 70's. Most of the Mullard app note scopes were valved units


Cheers, Ed

[djrm]

Hi
The inverter is interesting as I was asked to repair one recently with no success, it's for an artificial horizon out of an aeroplane. I believe it's 400 hz and AC outputs.

Hi David, sounds like a grand day out ! Birketts also was a good source of a/c stuff

Ferranti and others made standby inverters to work off the 28vDC supply, it may even have been a standard design. Useful bits of kit for all sorts of synchro applications

Scope looks interesting, it could be a WW design from the 70's. Most of the Mullard app note scopes were valved units


Cheers, Ed

Greetings, I was wondering if the unit would be able to supply the three phase motor of a gyro in the artificial horizon. I found a capacitor and inductor in the AC output circuits which are providing the phase shift needed to simulate a three phase supply. The photo shows a lamp load between three output pins of the inverter. One phase is much stronger than the other two but from past experience I think this would drive a motor, sweet. I'll try it on my old sperry artificial horizon. 45 watts are drawn from the DC supply in this test with three 110 15 watt bulbs connected.

   
 
The reverse engineering of the circuit and connections is coming on nicely now.
David.

[Dave Simpson]

Its great to hear that Birketts is still going well. Is it Mr Birketts daughter who runs the shop, or his son & his wife Ivana? I seem to remember that Ivana was running an online facility mainly for flogging their huge stock of ex RAF AP's. What - 10 or 15 years ago ?

                                     Regards,  Dave

[joebog1]

Dave,
Are ex RAF, AP's ex airline pilots ?.
Or dont I speak pohmie that well ? :-)

Joe

[djrm]

Its great to hear that Birketts is still going well. Is it Mr Birketts daughter who runs the shop, or his son & his wife Ivana? I seem to remember that Ivana was running an online facility mainly for flogging their huge stock of ex RAF AP's. What - 10 or 15 years ago ?

                                     Regards,  Dave

There was a man and woman in the shop, the woman told me she is Mr Birketts daughter, I told here I owed a debt of gratitude to places like theirs in developing my interest and later career in electronics. I'd seen here at shows in the past. I don't know about the man. When I was (even) younger I used to visit a similar place in Leicester - Eley Electronics. Eley's was a regular meeting place for the local electronics community with people like myself spending hours there browsing chatting, and sometimes buying. I understand that Mr Birkett and Mr Ely used to attend the same Govt surplus auctions. I used to have a morse coder training manual written by Mr John Eley.  I never mastered morse code though, its all I can do to tap out name. More recently I built a little gadget to decode my morse typing and display the result on a small LCD. see attached photo. end waffle