My To-Do List

[Mike H]

My 'To-Do' List (projects pending)

Someone posted recently 'I have too many projects!'
and I thought yes I have a few too, and then I thought maybe I should make an organised list. Most of these are/were 'progressing' at a glacial pace, also I keep changing my mind. Notwithstanding, and in no particular order...


#1. EL84 push-pull revamp
Status: finished
Start date: September 2023 (revamp)
Original build: May – June 2016 (according to photos' dates)


#2. 801A SET
Formerly known as: 'Aurora-7' (version 7)
Status: back-burner
Start date: October 2018 (according to earliest photos)
Parts: yes – a new wood box/case, nice new Schaeffer top panel, other parts recycled from previous. Will it be named Aurora-8?


#3. Fg810 Amp (a working title, from 'Fig. 8.10' out of a book)
Bipolar push-pull power amp, old design, 1960's - '70's
Status: in progress
Start date: 03/04/2023
Parts: very old 1970's style wood sleeve case that I want to use, that I bought, er, back in the 1970's, advert in Practical Electronics, never really used except once for an amp & FM receiver combo my dad used for a while.
Just ordered comps from Hi-Fi Collective and RS. Sims well in LTspice.
Pretty sure I made this in germanium, but there was only ever one board, I balls'd it up by not understanding how NFB works, left out a couple of parts, so it had no Voltage gain. To be fair tho it was one of the very few SS amp boards I made in those early days that didn't immediately catch fire when first turned on, and even more impressively, kept on working. Haven't got it anymore, of course. So it's kind of 'unfinished business' ...

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The wood sleeve case...

Wood sleeve case.jpg (130.05 KiB) Viewed 3180 times

[Mike H]

#4. MOSFET push-pull power amp
Status: stalled
Start date: 08/11/2019
Parts: nice case, MOSFET's, some other bits. Got bogged down with op-amp designs made from discrete components (based on, Wireless World article, 1972). It was all getting too complicated and not a lot of available space to put stuff on boards. This was going to be based on the Wireless World 'Texan', which later appeared in Practical Electronics as the power amps for a quadraphonic system called the 'Rondo' (where do they get these names).

The 'nice case' ....

MOSFET amp case.jpg (108.76 KiB) Viewed 3178 times

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#5. 'Transis-tronics Phono Pre + DIN Amp'
Status: in progress
Start date: 11/09/2021 (when case was bought)
Parts: Cute wee box. Comps from Hi-Fi Collective and RS, other bits.

Picture of cute wee box...

pre-amp case.jpg (90.02 KiB) Viewed 3178 times

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Transis-tronics was an American manufacturer during the 1960's. The circuit I copied out of a book in the 1970's, but never built. Curious what it's like. It works well in LTspice.
The 'DIN Amp' part is taken from the Akai reel-to-reel recorder, so-called because it's the input stage of the record amp board, 'DIN' meaning that originally the input was a 5-pin DIN socket (removed by previous owner and replaced with 4 dodgy phono sockets, which I need to do something about). Sometimes I need a bit more gain, if the source level is low, just a few dB, not a lot. The DIN amp will get about 12 dB or so. Switchable between phono and line.

[Mike H]

#6. Valve Oscilloscope Project
Yeah yeah I know I know, what's the point — well what's the point of messing about with old valve stuff anyways... this is a long-term itch I've wanted to scratch ... my first 'scope was homemade from a book, probably published by Babani or someone like that. In more enlightened hindsight it could have been done better, for example the deflection amplifiers were single-ended not balanced push-pull, and the timebase was minimal, but to be fair I think the author was trying to keep it as simple as possible for the home constructor. If nothing else it introduced me to 6SN7's. It was handy to have tho, and better than no 'scope at all. The 'new' design is closely based on the Heathkit OM1. All circuits sim very well in LTspice, even the timebase in each of its 4 sweep ranges, along with the overlaps using the variable pot at max. & min. positions. Deflection amplifiers are long-tailed pairs, and CCS's in the tail will improve the gain.

Status: back-burner
Start date: December 2009 (when CRT was bought)
Parts: Lots – started with finding a Russian CRT on eBay, then escalated (somewhat alarmingly) to include a posh Schaeffer engraved front panel, aluminium chassis parts, expensive comps from RS & Mouser & eBay, e.g. stackable wafer switches, mica caps, knobs, rare NOS 10 Meg pots, that kind of thing. So I'm financially committed!

Schaeffer panel designer exported image of front panel...
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om1-clone-panel2.jpg (36.28 KiB) Viewed 3178 times

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The CRT... I assume it works, I know the heater does which is always a good start...
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CRT 8LO29i-1b.jpg (42.03 KiB) Viewed 3178 times

[Mike H]

#7. Kubelik DAC
Status: collating parts
Start date: October 2023
Parts: board kindly donated by Ray P. JLsounds module arrived by FedEx today.
Will eventually need a case for it of some sort, power supplies etc...



#8. Much More Betterer Bluetooth Receiver.
Status: collating parts
Start date: September – October 2023
Parts: now have '4.1 5.0 Audio Receiver board'.
Bluetooth is useful because it's wireless. For a while I have been using the KRC-86B board which is all over the Internet & eBay. Now that my equipment is getting better, I detected an artifact which I believe to be, what I call, 'capacitor mush'. There are DC blocking caps in the signal paths somewhere, but I haven't yet identified exactly where they are, but they are undoubtedly SMD. The whole thing is too involved anyway, there's a multiplexer chip (i.e., a solid state stereo selector switch), and at least one dual op-amp. (And 2 other 8-DIL chips with no markings.) The idea is that there is another, 'default', stereo audio input, but when the receiver establishes a Bluetooth connection, it switches over to Bluetooth audio. The module is intended for Bluetooth speakers, apparently. I don't need that much complexity and so then I found a different board, that just has audio straight out of the chip, via a couple of easily accessible caps. Which could be bypassed...


"I have a cunning plan my lord..."


The ubiquitous KRC-86B on a motherboard which provides 5V regulator and sockets.
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KRC-86B Blutooth Adaptor.jpg (37.7 KiB) Viewed 3177 times

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Alternatively the 'Bluetooth 4.1 5.0 Audio Receiver board' has easily accessible audio outputs...
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Bluetooth 4_1 5_0 Audio Receiver board-2b.jpg (37.13 KiB) Viewed 3177 times

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Of course nothing is immutable ...


ENDS

[Ray P]

#7. Kubelik DAC
Status: collating parts
Start date: October 2023
Parts: board kindly donated by Ray P. JLsounds module arrived by FedEx today.
Will eventually need a case for it of some sort, power supplies etc...

I'll be dropping off the Kubelik package at the local postal depot this morning Mike.

I've included a couple of small toroids and some power supply boards for the the DAC and the JLSounds - you'll have no excuse for not getting it up and running! The power supply boards aren't fully populated, you'll need rectifier diodes and regulator chips to complete them - with what I've included you'll be able to power the DAC and both the dirty and clean sides of the JLSounds with linear regulated supplies. I'll dig out the schematics for the supply boards later for info.The epoxy centre of one of the toroids came apart so you'll need to devise a means of mounting it to the chassis.

Nice chassis for your Mosfet amp BTW, I've been looking at similar types for a Nelson Pass ACA (Amp Camp Amp).

[Ray P]

Linear PS board info attached Mike.

[Mike H]

#7. Kubelik DAC
Status: collating parts
Start date: October 2023
Parts: board kindly donated by Ray P. JLsounds module arrived by FedEx today.
Will eventually need a case for it of some sort, power supplies etc...

I'll be dropping off the Kubelik package at the local postal depot this morning Mike.

I've included a couple of small toroids and some power supply boards for the the DAC and the JLSounds -

Ah wondered why I had so many. Coolio!

you'll have no excuse for not getting it up and running! The power supply boards aren't fully populated, you'll need rectifier diodes and regulator chips to complete them -

Yup, should have some regs kicking around somewhere, LM317? If not, easy to get...

with what I've included you'll be able to power the DAC and both the dirty and clean sides of the JLSounds with linear regulated supplies. I'll dig out the schematics for the supply boards later for info.The epoxy centre of one of the toroids came apart so you'll need to devise a means of mounting it to the chassis.

Righty-ho chief. As it happens, I concocted the mad idea of cable-tying them onto prototype board – no screws needed then...

Nice chassis for your Mosfet amp BTW, I've been looking at similar types for a Nelson Pass ACA (Amp Camp Amp).

Cool innit. Chinese off-of eBay.


The apertures in the wood sleeve case are such odd measurements (actually, imperial, to a 1/16th inch) it occurred to me to have Schaeffer panels made to the exact dimensions...

[Mike H]

Linear PS board info attached Mike.

Again, ta muchly....

[jack]

I had a Heathkit OM1 that I made back in the '70s. That screenshot bought back a LOT of memories.

I have no idea what happened to it - I've mislaid a number of tea chests of stuff over the years so I suspect it was in one of them, along with a load of early sci-fi as I can't find a whole load of Asimov, Dick, Clarke, Lem, Pohl etc.

[Mike H]

Thanks Nick, interesting.

It was a friend in 6th form at school who first got me into this electronics lark - we both got a Heathkit stereo record player each (I used to bring mine into the common room for anyone to play records at lunchtime), then he started looking at getting a better turntable for his, then better speakers (homemade, we're still poor students). Then he started talking about replacing the amplifier and thus began the slippery slope (for me at any rate) of trying to make germanium transistor circuits work. Altho he wasn't quite as poor as the rest of us, as his family ran a newsagents shop and he always seemed to have more expendable funds. E.g. he was the first kid in our form to have his own car. Admittedly it was a 2nd hand Ford popular 100E, but even so - his own car!

He could also have some nice electronic gear, and one day started telling me he about building a Heathkit oscilloscope kit. I was well jealous. It cost a lot if memory serves, altho Heathkit was never really cheap.


All kinds of (other) stuff has been going on here so not been posting lately - but Kubelik DAC is at the front of the 'to do' queue - at least for now ... another I'm working up to is the so-called 'Fg810' (schematic copied out of a library book circa 1972 -ish). New topics should appear in due course.

Laters!.....