Ameritron AL-811HXCE valves arrive

As per previous blog I got hold of some NOS - New Old Stock RCA 811A for the 811HXCE. I've already got some russian copies but wanted to get some reasonable ones for testing and have had great experience with RCA's.

They arrived, very well packed and they were better than I could have hoped, boxes a little used looking but inside original packing and lables (always a good sign !!).

Here they are (well one of the four anyway !!) :-

Ameritron AL-811HXCE - Components arrive

Well, the postman's been busy this week :)

Arrive home to find a small package, which contains my larger doorknob capacitors that I purchased. I was pleased to see how carefully they were packed - padded envelope and within that a small plastic box, and within that some more bubble wrap !! 

When opened, I find (somewhat confusingly !) four capacitors - the two I ordered and two extra, only after checking the packing note did I realise that the extra two were a free gift from the shipper - bonus ! 

The quality of the doorknob capacitors seem excellent, as expected these are Russian made but measure correctly and are new and unused.

Superb packing !!

Ameritron AL-811HXCE back to life - part 5

So, having made the PCB (see part 4), now comes the time to populate it. Parts arrived fine from Farnell, and the capacitors of a similar type from another UK supplier.

I'm not keeping a total of parts spend on this - (if money was no object then I would have simply sent it for repair[no fun or challenge in that!!]  or got the bits from Ameritron in the states - look back at my earlier posts - this is not cheap!) - anyway I think as amateurs we can all improve/build on each others work, and definitely improve on commercial designs, where sometimes quality is compromised for ease of production or make slightly more money.

So wound the coils, and put the coils and 5w 100R Resistors in, and then put the braided leads on for the anode caps. 30 minutes of construction results in a new parasitic board.

Here it is -

Not too shabby really, in my humble opinion, if you consider what it was like before (look back in the blog) and now after a total rebuild, there is no comparison in my opinion, a major difference is that I hope that this one will work :) - anyway two major elements completed, the choke and the parasitic board, so onward to component improvement and rebuild, then test !!

Nearly there !

Bringing an Ameritron AL-811HXCE back to life - part 4

So....

Rewound / rebuilt the choke (see part 3), and so now onto the parasitic board. Now this was very badly burned up, carbon in many places as you can see from the pictures (apologies about the quality of these!). The odd bits of wire coming out of either side are actually the HV feed to the 811a anodes cap and yes you've guessed it, they are badly over heated / damaged.

So now I've got to make another one. 



As you can see from the third photo (what is meant to be the copper side) it was in a very bad way

Anyway, I thought I could see where copper should be and that together with the circuit diagram and some interpolation gave me a bit of a head start.


So I removed all of the components from the PCB and then carefully looked at what was left. The short answer was not much !!!

But it still had holes, so first step was to get some paper, place the board on it and then use a thin instrument (I used a long drawing pin!) to punch through holes to give me a location of where the component leads should go. From there I looked at the damaged board very carefully and slowly reconstructed where the copper should have been originally.

I then used this to transfer the tracks it onto a Copper (Single Sided) PCB substrate, using a combination of rub on transfers and PCB etch resist pen. I then etched this in the normal way for making PCB's using etching fluid, there plenty of web pages that show how to do this so I wont bother.

Anyway the result is shown in the fourth photograph  with the other (original board) shown below - just a little different !!! . This shows the copper side, and the odd black squares you might able to vaguely see are on the non copper side and mark where the components for the board should go so I don't forget.

I then drilled the board with suitable holes (the coils and resistors need a larger hole than the capacitors. 

I then looked at the components I had taken from the amp, I carefully measured them and (somewhat unbelievably) they all measured OK !! - Anyway the PCB cost me nothing and goodness knows how many heat cycles they had been through, and they were bound to fail sooner rather than later so I decided to get new components and of course wind new coils.  The components have been ordered and should be with me in a few days. I've already wound the coils and found some decent braid to use for the four connections to the anodes, so the assembly should be a nice straightforward job when they arrive.


I've also order two lovely doorknob capacitors from the Ukraine (again courtesy of eBay) which are 2.2nf (2200pf) 10Kv. One of these I will use to improve the blocking capacitor as per the article from DC9ZP. The original one is 3 - 4Kv I think. They look great on the web, I await their arrival with interest.

On the subject of High Voltage components, has anyone noticed how many items (especially above 5Kv) seem to come from the ex soviet union / Baltic states - wonderful quality and (I think) great prices - even after paying import duty. Its definitely worth considering them if you need such things in my opinion.

Until next time 73's

Another eBay purchase - Ten Tec Omni V

Here's the latest arrival for repair / renovation at the shack - A Ten Tec Omni V - This one looks in poor condition  ( not sure how it was stored but bits are rusty, and its very dirty and dusty ) - sold as " faulty receiver needs work, display OK, no transmit " - I got this from an eBay seller who I trust 100% - I've bought plenty of non working stuff and he is always accurate in his descriptions.

As described in others posts, I always check before applying power (yes even 12V !) internally for obvious problems or damage. The seller had already tried it to check the receiver and display, but I still check anyway - better to be safe than sorry.

If you look carefully at the picture (left) you will see what I'm working with - look at the knobs - very dirty, full of dust. I can't really describe how gritty they felt both to touch and when I turned them !!

The picture to the right shows  the other side of the transceiver, again look at the main spinner, again very dirty, and very very stiff to turn and the keypad has paint on it (white flash in the middle of the picture just above the blue M -> VFO button, again the buttons were very grubby and didn't feel very good at all.

From a distance it doesn't look too bad does it ?  but looks can be deceptive :)

It didn't come with a microphone or power cable (was described like this)

When I checked inside I got a very pleasant surprise ! - firstly looked in good nick, is very well built and had all its shields and screws intact - this is not always the case with eBay purchases - especially if someone has "had a go" at repairing it. The next pleasant surprise was it was fully fitted with all the filters that can be selected from the front panel - wow !!!!

This one looked like it hadn't been touched at all - just stored for a long time (probably in a garage or a loft !!) - in fact absolutely perfect for restoration :)

Bringing an Ameritron AL-811HXCE back to life - part 3

Have some time off this week and so got some more done in the shack and so, As per blog part two, ed work on the 811, first thing to do was count the windings.

This was not as easy as it first sounds.

I didn't want to remove the windings immediately, but count them on the ceramic former, belt and braces I thought.

In the end I resorted to using a head mounted magnifier (you've got one of those haven't you ? - if not get one, I use it for surface mount construction and repair but it's really useful for lots of other things !) to count them. 

After some experimentation - I developed this technique - using a pair of fine tweezers that I have for surface mount (I also tried a cocktail stick - didn't work as well) I dragged it across the coil (very lightly) to give me a little tactile feel (click) for every turn whilst I watched very carefully, and I do mean carefully.

I did this in a quiet room, with no-one else in the house as it really needed concentration and no distractions - but that might just be me ! 

I did this three times to get an average 

I then removed (unwound) the former to see if I was right (a further double check). 

I then checked what the SWG of the wire was (removing the enamel) and measuring the wire itself - you did know that SWG is measured without insulation didn't you ? I didn't until I read about it !! Thus turned out to be 18SWG - and luckily I have some in "stock" and so  after a little consideration, and a careful marking of the former where windings started and finished - and more importantly if you read Tom's article, where the gaps are and then started winding..

The result is shown below :-

Apologies for the worktop :) at least it shows it gets some use !!!

And this is the MiniVNA plot for TL which shows where the various resonances are :-

As you can see the peaks are out of the amateur bands (main peak at about 12.4Mhz), there does seem to be one quite close to 17M (one of my favourites), when I ran the same check centred on 17M there was no resonance / problem shown, so should be OK I think. It would be good to check an original one, it is interesting to note that Tom W8JI in e his RF plate choke article talks about resonance on his original choke that went into the Ameritron was at 12.5 Mhz, and so mine seems to be close which is good news!

Also I not that there is a hand written 12.9 on the original coil - possibly this is its primary resonance ? anyone know is this assumption is true ?

I've also measured its inductance as 222 uH which seems to be quite close to one very similar on Tom's site which is 245uH - so again pretty close methinks.

Also the spare in the RF Parts catalog shows its inductance as 235 uH which again is not to far off.

Not too shabby for an approximation, reverse engineering a burnt and broken coil :)

Onwards to the parasitic board reconstruction .......

Ameritron AL-811HXCE back to life

Good news !!! - just acquired from eBay four RCA - NOS (new old stock) 811A 's from a UK seller - I got hold of some russian ones a month or so back just in case - but RCA at a good price (and I do mean good - thanks nick!) I couldn't pass them up could I ? 

Hope the arrive safely, (and work of course!) but that a risk from wherever I got them from.

Anyone out there have any advice on how to "burn them in" - or whatever the equivalent is ? 

Now just go to get on with fixing the amp :)