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Old 17th Sep 2017, 11:17 am   #241
Diabolical Artificer
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Default Re: 807 (maybe) amplifier build. Now EL34

Here's the schematics for the amplifier. There is the odd drawing mistake.

Thankyou Joe, your appreciation/support is welcome.

Am aware of inefficiency of speakers David, the weak ling in the audio chain, or one of em.

Thanks for pointers Chris, I'll tackle it one day in the week.

I've personally found that after about a watt or so, my ears can't really detect any incremental increase in loudness. The main joy of listening to loud music is the bass hitting you in the guts, turning your diapragm into a driver of sorts. I end up with a girt big silly grin on my mush for some odd reason. Maybe this is an atavistic reaction to do with drums.

Anyhoo, I digress. Re, the amp etc circuits; any thoughts, comments or constructive criticism welcome.

Andy.
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Old 17th Sep 2017, 11:54 am   #242
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Default Re: 807 (maybe) amplifier build. Now EL34

I have the schematics as a Docx file which is too big to upload here. If you want it drop us a PM with your email address, and I'll send it to you.

A.
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Old 17th Sep 2017, 1:42 pm   #243
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Default Re: 807 (maybe) amplifier build. Now EL34

A few notes on the PSU schematic. The voltage at the tap on the cathode follower htr supply is 200v. Oh and there are 0.1u caps accross the 12.6v htr supply, bias supply bridge rectifiers to stop switching noise. Same as on the HT supply BR's. The "symbol is a conflation of a BR and N suppression caps.

A.
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Old 18th Sep 2017, 1:24 am   #244
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Default Re: 807 (maybe) amplifier build. Now EL34

Hmm I think 18.9 volts for 2 X EL34 is a bit high too!! Maybe you mean 3X EL34 ??

best regards
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Old 19th Sep 2017, 9:10 am   #245
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Default Re: 807 (maybe) amplifier build. Now EL34

That's 2 x 18.9v for six EL34's Joe, three each side.

A.
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Old 19th Nov 2017, 9:33 am   #246
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Default Re: 807 (maybe) amplifier build. Now EL34

I've been busy since my last post and have made the left ch monoblock chassis, wired it up and made another protection/VU driver/etc PCB, as well as fabricating panels for the top of the amp. Also spent weeks faffing about with spray can's and spending a small fortune on paint tying to get a good finish on the chassis and top panels. This has been a frustrating exercise because though it's possible to get a mirror finish with cans, in practice, in a home environment, it's nigh impossible. At this time of year the pieces your painting have to be warmed up, as does the paint can itself. I started spraying in the living room with all the doors open. Despite paper on the floor I managed to spray the rug and carpet. The finish was crap,with the dreaded orange peel texture. So, lot's of rubbing down followed. This is tricky to do on sheets with edges, cos if your not careful, you sand the edges back to metal. This after about a week of applying filler to get nice rounded edges on the vent's. I'm a bit OCD so tortured myself trying to get the curves perfect, each one the right width and curvature. Nightmare!

I also spent five days trying to make 4 brass D handles. Some time ago I bought two brass D handle's for the front of the monoblocks to pull them out. The seller had 100's at the time, so I bought 2 and thought I'd order another pair if these one's were ok. They were, a few weeks went by, went to reorder, out of stock!. There then followed weeks of trying to find a match. Most 4" brass D handle's are of a smaller dia than "the pair" and had shorter fixing centre's. In the end I bought some 3/8" brass bar so as to make my own. Big mistake. How hard could it be to put two 90 deg bends in a bit of brass bar, 102mm apart? Well, with only the house fire as a source of heat it proved to be problematic. I tried several jigs, bits of pipe to ease bending, tried whacking the F%$ out of it with a wooded mallet and after one day, got one handle with the bends the same and the right distance between fixing centre's. Next day tried again, getting better, but no, result was different. The problem was I'd already drilled the front panel's, and painted them. so back online to try and find any four matching brass D handles, re drill front panels etc, etc. Onto ebay, b*gger me, the seller had restocked, there were the exact handles I needed. Sheesh, good job I have a sense of humour.

Back to the paint job... in the end, I ended up painting the case with dark green Hammerite which looked ok at first, but with a second coat I could see imperfection's, brush strokes. I was about to rub it all down yesterday and thought enough! Your never going to get it 100% perfect you eejit, on with the job!

So the last pic shows the wiring in of the mains socket, fuse holders, small transformers etc. I've put sleeving on the mains IEC socket even though it will be not accessible to fingers and it was a b*tch to do, still, you have to do the job right; details, details.

I'm still not happy with the paint job, notice the dribbles on the inside, but if I faff around any longer, I'll be here to next Xmas. Next time I'll pay someone to powder coat it, lesson learnt.

Andy.
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Old 19th Nov 2017, 11:04 am   #247
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Default Re: 807 (maybe) amplifier build. Now EL34

Hey Andy, I feel your frustration over the paint job! I get a feeling of how high your standards are, and I can’t apply paint perfectly for toffee!

It’s a great project and I hope you can now put your feet up and enjoy the fruits of your labour for a while!
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Old 19th Nov 2017, 11:58 pm   #248
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Default Re: 807 (maybe) amplifier build. Now EL34

Many years ago I discovered that spray cans are for car suspension parts NOT amplifiers!!!!

I bought a small Chinese compressor, and a half decent Chinese spray gun. $125 or about 70 quid for you.
A litre of hammertone costs about $40 Australian, one litre is enough to paint 20 LARGE chassis. To make a really nice job, you can use spray bog as a filler and sand down to suit your taste.

Several millenia ago I used spray cans in the house and mum chucked a REAL wobbly!!! and I didnt spray the carpet .

I am spoilt I guess as its about 30 degrees C for most of the year, and I dont have the English rain and cold to deal with. I do however have native Australian bees!!! They just LOVE drying paint to die in!!. This leaves "leg ends" stuck in the paint after its dried and I rub their bodies off the surface.

To beat this ( AND it will protect your carpets) I go to the supermarket and get a LARGE cardboard box, ( a fridge box maybe ?? ) that I lay on its side, with the open end facing me. I stick a couple of holes in the top and use mig wire ( ONLY because I have it) to hang the chassis/parts to be painted. A heavy chassis will need a wooden rule on top of the box to spread the load when the wire is wrapped around the rule. Spray inside the box.

An alternative to hammertone is "satin" enamel!! I use "Killrust" brand. It tends to hide small defects, and doesnt run easily. Its available in spray cans too!!.

Keep up the good work

Joe
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Old 20th Nov 2017, 7:38 am   #249
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Default Re: 807 (maybe) amplifier build. Now EL34

Quote:
Originally Posted by astral highway View Post
I get a feeling of how high your standards are
Not really high, just things bug me if they're not right. Also thing is Al I've worked on this for a year and it'd be remiss to bodge the finish. It is harder to do decent job's when painting say, if you don't paint every day. Towards the end I was starting to nail it and was getting better.

Should have the PSU wiring done by the end of the week, so am nearing the end. It'd be nice to finish just so I can start another project or make inroads on the rountuit pile. Last hurdle is I need to find the dosh for the LH Ch OPT and order it from the states.

A.
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Old 20th Nov 2017, 8:31 pm   #250
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Default Re: 807 (maybe) amplifier build. Now EL34

Hi Andy.

That amplifier project looks really good to me! Power to your elbow mate. I will be very happy when my fairly ordinary, in terms of circuitry, "modern day" Leak mono amps are again up and running with the offboard psu, or if that fails a total rebuild on a single chassis.
Anyway, i had never spray painted anything in my life until a couple of years ago and although my efforts would never come close to yours, I think I made a reasonable fist of the job with spray cans. But i found in the local LIDL supermarket a nifty little device that clips on top of a normal "rattle can" and allows you to hold it like a proper spray gun> this allowed me to control the spray quite well and avoided the painted index finger too! I imagine you could find one of these gizmos online or by hunting around. I need to paint up the ally chassis for my psu to match the amps and I am not looking forward to it as now the temperature and humidity levels are just not good.
I also usually give a few coats of transparent lacquer once I have a nice uniform colour coat as It seems to give the finish a harder wearing property as well as looking nice.

Andy.
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Old 21st Nov 2017, 8:39 am   #251
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Default Re: 807 (maybe) amplifier build. Now EL34

I do have a little nailgun compressor and a gun, but no pipes to connect them. I've also shied away from getting the paint due to the expense, I think you have to buy about 5L and your talking getting on for 100! But obviously it keeps. What is "spray bog" Joe? Still, I ought to invest in in the proper kit and paint. The lacquer I'm using is problematic too, (HK 2K), that really stinks the house out and makes you dizzy, as well as not completely setting. I sprayed all the bits, got a good finish, put all the bits between sheets of newspaper to protect them, next morning the paper had stuck to the bits. More rubbing down, oh joy.

Yeah, insects, I run round all the time trying to save them if they fall in a bucket of water etc, then they go and land on your paint job, sheesh. Our bees are more intelligent on this side of the planet, it's the little fellas that seem attracted to paint.

Bless you Andy! Wish I did have powered elbows, some sort of cyborg suit, would help with all the rubbing down. : ) As mentioned above, I'd do some research on lacquer types.

Here's a pic of the amp front, note dark green ( BRC) that it should have been. It does match the Hammerite case though. I thought it would look good with the brass handles and brass cinching knob.

I had a right to-do with the meters too. I found and bought two NOS 50uA identical meters that some couple found in a cupboard when moving, still in their MOD packing. Fitted one, all good. Tested second, aggghhh, open circuit! Opened it up, no obvious loose wires. My fumbling fingers were too much for the workings, it ended up in the bin, but then thought better and fished the bits out. I searched and searched for a twin, to no avail. But after months of searching I spotted an indentical movement in a meter on ebay. Totally different meter case. Anyhoo, to cut a long story short, I fettled the two meters by swapping parts. Had to cut the needle off the new one as it was too high, but managed to super glue it on. So the meter looks identical, but the new one is 2mA FSD, not 50uA. Fortunately, with a shunt on the 50uA and a VU driver that can be adjusted they move the same, ish.
I just have to figure out how to use Gimp so I can print off a VU meter scale.

Andy.
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Old 17th Dec 2017, 1:40 pm   #252
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Default Re: 807 (maybe) amplifier build. Now EL34

Bit of a disaster here in big amp land. Having spent the last few weeks wiring up the second PSU for the LH channel, I went to do a test of the front end and driver, after making sure I had HT etc where it should be. Put a signal in the front, no sig out, so started taking some voltages. I'm getting 12.1V for the heater power supply, should be 12.6v and getting 434v HT, which should be 490v unloaded.

So checked the V before the LM317 = 13.5v, which is no good as drop out V for a 317 is around 1.2v. Checked the mains V = 242v. So therefore, unless I've missed something, I've really cocked up when I wound the tfmr. The thought of taking everything apart and unwinding it and starting again is not appealing.

Surely I can't have cocked up this badly? I can't find my notes at the moment, but I'm wondering if I got a bit blase' and wasn't as careful as I was the first time round. Will investigate.

Andy.
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Old 17th Dec 2017, 9:49 pm   #253
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Default Re: 807 (maybe) amplifier build. Now EL34

Hi Andy, did you add "compensating turns" to your transformer to allow for pri & sec winding resistances at max current draw?

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Old 18th Dec 2017, 8:34 am   #254
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Default Re: 807 (maybe) amplifier build. Now EL34

I did Ed. On further investigation yesterday there is something weird going on with the 12.6v regulated supply. It has a too low AC IP; @ 10v it should be ok, just, but is on the low side. This gives us 12.1v regulated, I may be able to steal a few volts from another winding, or use a voltage doubler instead of the bridge that's there, a bodge though - fixable though annoying. I over corrected on this tfmr, on the RH one I wound for too much IE 15v AC = 21v DC. The the wire gauge I used is thicker than needed and the PSU only supplies 300mV, so I didn't invisage much V drop. The odd thing is that when connected to the amp chassis the OP of the htr PSU drops to 1.1v, this is without a valve in the socket, very odd. More investigation needed.

I'd made a boo boo when wiring the relay on the soft start so that with the relay off, the R was switched out, relay on the dropper R was permanently in circuit, hence V drop. So I was one pin off on the relay socket. This improves things, but after checking the other PSU, AC off the tfmr is the same, EG 179v, which should give around 250v DC or 245v after the bridge rec diode drop is taken into account, wiring losses etc. So that should give us 490v unloaded. However, 179v goes into the bridge rec, 232v comes out the other side, so the bridge is dropping around 12v or my sums are really out.

I have some more checking to do today, it could be I've done something daft. It's busy in the PSU compartment, wires everywhere and my eyes arn't brilliant. Add to that my brain doesn't boot up fully some days and a mistake was likely. At least I may not have to rewind the tfmr again, panicking there for a second.

Andy.
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Old 18th Dec 2017, 9:39 am   #255
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Default Re: 807 (maybe) amplifier build. Now EL34

Hi Andy, possibly the best method would be to take all sec leads off both transformers and power them up. Do a winding by winding comparison and look for differences.
You should also look at the transformer primary magnetising (no load) currents and differences in heating. The clamp bolts you have used may not be sufficiently insulated from the core and ensure that the lams are butted together with a minimum of gaps.
Both of these will increase mag current and output volt drops.

Ed
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Old 18th Dec 2017, 11:10 am   #256
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Default Re: 807 (maybe) amplifier build. Now EL34

Thanks Ed. The tfmr is actually a toroid, taking some readings as suggested. The mistake I've made with the htr PSU is to use 1.414 to get my DC RMS and not allow enough V drop for the bridge rectifier I think. I've just measured some voltages, I have 10.9v AC from the tfmr winding, I reckoned on getting 15.4v DC RMS, but am actually getting 13.7v, so that is not enough headroom for an OP of 12.6v for the LM317. Reading online, 3v is suggested.

On the 317 datasheet there is no dropout voltage as such, it's called the IP/OP differential. This vary's with current and temp, but should be about 1.5v, which adds up.

So what is going on here? I reckoned for a V drop of 1v for the bridge (datasheet says 1.1v), so obviously 1.414 is not a good "enumerator" to use, 1.2 would be nearer the mark. Does this mean that there are actually 4 1v drops to take into account?

I measured another PSU, this for the DC PSU/soft start circuit. With 52v AC, I'm getting 69v DC. So 52 x 1.414 = 73.5v getting 69v, therefore if I'm right the bridge is dropping 4v in total or there is another explanation, meter error for example.

Andy.
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Old 18th Dec 2017, 2:40 pm   #257
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Default Re: 807 (maybe) amplifier build. Now EL34

Andy,
I use 1.36 for solid state rectifiers and 1.29 for glass rectifiers, if that helps?
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Old 27th Dec 2017, 9:32 am   #258
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Default Re: 807 (maybe) amplifier build. Now EL34

Thanks Howard. I've been doing some reading up as well as a few experiments so that in future I have something better to go on.

Andy.
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Old 27th Dec 2017, 11:20 am   #259
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Default Re: 807 (maybe) amplifier build. Now EL34

A bridge puts two diodes in series with the winding, so you get two diode drops.

A capacitor input reservoir charges only on the peaks, so the current outflow has to be made up in short sharp bursts. So the diode drops are those appropriate to the greatly exaggerated charging current pulses. Also copper losses in the winding and wiring are similarly scaled up.

Calculations with correction factors are serious over simplifications because you are looking at the integrals of oddly-shaped pulses.

LT spice with carefully modelled 'strays' will get you there and show you what's going on.

David
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Old 27th Dec 2017, 1:26 pm   #260
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Default Re: 807 (maybe) amplifier build. Now EL34

Maybe load the secondary winding up first to give the current you require and see how everything sits.

The peak voltage of the DC pulse out of the rectifier will be approx. peak volts in minus 1.2, 1.2 being the approx. voltage drop of the diodes in the bridge, from that you should be able to get a ball park figure for the average DC voltage expected across the load by doing a quick calc....Vdc = (approx.) Vp - I/4Cf

Where Vp = Peak AC - 1.2 (Volts)
Where I = load current (Amps)
Where C = Reservoir capacitance (Farads)
Where f = Supply frequency (Hertz)

For a ball park ripple voltage calc. for a bridge at 50Hz V = 10*I/C

Where V = Ripple voltage (Volts)
Where I = Load current (mA)
Where C = Reservoir capacitance (uF)

Lawrence.

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