Jumping back in...

[kennyk]

... This time I'm going to complete a project.


I've got two projects sitting, untouched for over a year. So I've decided to complete one of them before the end of the year.

My two nemeses are
1) the 2A3 which I got as far as soldering some stage multicore between the selector and the phonos. I may even have done a couple of inputs... so that's not even completed. I've got well over 90% of the bits. I think it lacks for some tubes as well.

2) The 300B PSE not-quite-clone that I bought partially stripped from Dr John. I contacted Amythyst a while back for a quote for the missing OPTX but never got a reply and I just forgot about it. I tried again using a different email address and long story short, they're as good as ordered.
the lineup on this amp is EF86 - 5687 - 2 x 300B and 5U4G. I've got the 6AU6 and the valve holders, so the plan eventually is to convert it back to 6AU6 - ECC82 front end. In the mean time I just want to get something completed so for ease, sticking the OPTX plus re-attaching the chokes and sticking in some valves seems to be the way forward.

The only other thing I'm lacking is some 300Bs - I need 2 pairs, so if anyone has any recommendations about what's currently cost-effective and where the best bargains are (or wants to sell on some surplus / part used ) I'm all ears.

In truth I've had a whirlwind year, changing jobs from part time with 50 mile every day commute + crappy min wage extra job, to a full time much nearer job that I don't like nearly as much, so I need something to distract me from that. Now the clocks have gone back it's time to fire up the soldering iron!

My KEL84 has been in service for 8 years and it's time for something different...

[Greg]

There are several choices to be made when choosing 300B valves but if you are after a good lively and fully extended sound, you can't go far wrong with Electro Harmonix Gold Grid. Don't be tempted by their cheaper version which has a dull sound in comparison. I have used these for over ten years now, occasionally replacing them as and when they start to tire. I know several others who find them very musical and in 300B terms, good value for money.

ObviousLy check eBay for possible offers from Hong Kong, but otherwise, Best price in the UK is probably from Hotrox. Remember to order a matched quad.

http://www.hotroxuk.com/electro-harmoni ... -grid.html

[kennyk]

Thanks, Greg. I didn't know they had more than one type so it's good to know which version to get for the sonics, that look just about perfect in terms of budget too.

Once the trannies are on their way I'll probably get a set ordered up.

I've now retrieved the chassis from the loft and they're sitting handy to solder up the trannies when they do arrive. Also the chokes I've got are the standard WAD 300B PSE ones, whereas Dr John's chassis had all uprights under a rectangular cover so I'll need to do a bit of case modding to bolt down the chokes. Chances are the upright versions that Amythyst make for the OPTX won't match the mounting holes for the originals either so I'm holding off to do the whole lot in one go.

[Paul Barker]

...

In truth I've had a whirlwind year, changing jobs from part time with 50 mile every day commute + crappy min wage extra job, to a full time much nearer job that I don't like nearly as much, so I need something to distract me from that. Now the clocks have gone back it's time to fire up the soldering iron!
...

As this is part of the first post of the topic I claim discussion of the issues as on topic.

Speaking as a gypsie to the world of work all my working life including career changes at least every decade.

I made load of bad decisions and lots of jobs I left for greener pastures that turned out to be worse.

In the end I think: do your job to the highest level of skill of anyone within your sphere of reference. Don't leave a job on the things you see as negative about it, unless it is totally unbearable, because the negatives of the next job will probably be far greater.

Learn to be content.

And don't spend too much on this hobby.

[Alex Kitic]

In truth I've had a whirlwind year, changing jobs from part time with 50 mile every day commute + crappy min wage extra job, to a full time much nearer job that I don't like nearly as much, so I need something to distract me from that. Now the clocks have gone back it's time to fire up the soldering iron!

Make that a crappy boring full time job which is 30 min away from home (bus and walk in total) - with a nice title and lowly wage (even for local standards) - and we would be in a similar bucket?!

Having started some 2A3 amp, maybe you might transform it into an RH2A3? It could be a lot of fun and enjoyment for you, and it sounds great so it should be gratifying as well... and not cost what you might not want to pay...

[kennyk]

Pleased to say that the trannies have arrived.

I've drilled out the top plate to accept the chokes - the ones I've got are original 300B PSE ones rather than top mounting.

And the valves are on their way, courtesty of that link of Greg's.

The only things holding things up are the screws/bolts (now sourced from eBay and a spare evening to solder the chokes/ trannies into the circuit.

I still feel like I've cheated a bit on this one but, hey ho!

[Greg]

Keep us informed with your progress. Well done so far! I'd like to know how you find the amps once you've got them running.

[kennyk]

I've finally found some time to make a start. I've done one amp but so far it's not going well.

The valves all light up, but I'm getting nothing from the speaker, and my choke voltages are well over 500v although there is a small differential between them, I think they're 550 and 535.

As the amps are Dr John's own concoction, I don't have a full circuit diagram so I'm not sure where to start to be honest.
That said, they've not been powered up for long ( a couple of minutes max) and I'm wondering if there could be an issue with the NiCad for the battery bias, especially since they've possibly sat for a good while. I'm still very nervous of turning the amp upside down and poking around.

Any thoughts?

[rowuk]

Flip the amp over and take some clear pictures to upload here, maybe we can see something obvious.... If you have any circuit diagram at all, it would be helpful too.

There are tried and true designs that almost guarantee success. They are all well documented and there is original designer support available in many cases.

I built one of Alex's RH amplifiers and got incredible support. It worked from the first turn on and now we are not talking about engineering rather getting the most sonically out of it - support beyond the original build!

I've finally found some time to make a start. I've done one amp but so far it's not going well.

The valves all light up, but I'm getting nothing from the speaker, and my choke voltages are well over 500v although there is a small differential between them, I think they're 550 and 535.

As the amps are Dr John's own concoction, I don't have a full circuit diagram so I'm not sure where to start to be honest.
That said, they've not been powered up for long ( a couple of minutes max) and I'm wondering if there could be an issue with the NiCad for the battery bias, especially since they've possibly sat for a good while. I'm still very nervous of turning the amp upside down and poking around.

Any thoughts?

[IslandPink]

This is the WAD 300B PSE is it ?
The voltage sounds high - shouldn't it be 450 to 470 max ? - is that after the choke ? - B+ ?
Sounds like something , prob the output valves , is not conducting much .
NicCads on the voltage amp or driver, yes ? - they need checking yes, but would probably result in less bias, more conduction - not good, but not enough to have the PS sitting at >500V .

If you turn the whole thing upside down and stack up on old video tapes etc. so you can have the valves in and switch on, then it will be helpful . First thing to measure is where the grid and cathode voltages are on the output valves ; then same on the drivers or cathode followers or whatever it has.
You'd be expecting grids to be near ground and the cathodes about +70V for SE 300B's .

[Greg]

If you are struggling, my advise would be to go back and consult John Caswell. PM me if you need his email address and other contact details or raise your problems on http://www.world-designs.co.uk/forum/

[kennyk]

I've spoken with John, and am feeling a good bit less petrified!


so far -200v at the 300B grids. the 300Bs are fed by a 5687 and all the associated voltages are somewhat wild. the circuit, John tells me is 'lifted' from the glasshouse amplifier circuit. So armed with that information I've sourced and printed off the diagram.

I'm going to solder up the second amp and see what happens with that.

[kennyk]

bit more poking around has shown that the voltages settle down to more normal, apart from one. the anode of the EF86 is sitting at 346v instead of 195.

Both amps are the same, and I've tried two EF86 valves. Getting a crackle from the speakers when I touch the anode with a probe which is encouraging.

[rowuk]

A picture speaks a thousand words......

Too much voltage on the driver stage anode will not mute it. Wiring the EF86 up wrong could cause high voltage and no sound. The output stage sounds ok.

bit more poking around has shown that the voltages settle down to more normal, apart from one. the anode of the EF86 is sitting at 346v instead of 195.

Both amps are the same, and I've tried two EF86 valves. Getting a crackle from the speakers when I touch the anode with a probe which is encouraging.

[IslandPink]

So, there's something wrong in the cathode/grid area of the EF86 , causing them not to conduct much .
Have you worked out why the first amp had output valves with -200V on grids, which suggests the 5687 CF is not set up correctly ? - that would explain the PS being at over 500V .
What was the bias on the second amp's 300B's ?