807 Clementine Ultra build finished

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

807 Clementine Ultra build finished

Postby whaam68 » Sat Feb 25, 2012 9:28 am

OK finally done....big thanks to all those who chipped in with my questions during the build & especially Thermion! (JT). I followed my usual check out procedure....hook up....plug in....turn on....get ready to turn off! =:o Fortunately it just worked....which is nice....sounds real good....not quite as sweet as the GSG but definately more poke & I'd say tighter bass & definately a keeper. I built per shannons notes but as these are 15ohm outputs used a 1K in the feedback circuit (I also upped the paralell cap value to match...was this ok? 63v polystyrene cap). It's been on soak about 3 hours, outputs are pretty much cold, & power tx only warm.

Only two things I need a steer on...there is a small amount of hum once powered up that doesn't increase with volume not a lot but it's there...any ideas?

The bias meters are only reading 30ma...I'm sure this is low but the amp sounds full & pokey....did I wire these up wrong? both track the same & rise slowly with the thermistor. 807's are hot...to the touch

Ok that's it for now! I'm digging the ebay pimp up blue LED...I wired this up to the spare 6.3v taps...is this ok? it's got a resistor in line already for 6.3v operation.

Mike

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Postby Ty_Bower » Sat Feb 25, 2012 7:28 pm

Very nice. Love the plate caps. :)
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Postby whaam68 » Sun Feb 26, 2012 2:49 am

Cheers Ty. I'm pleased with the way it turned out....very flash gordon! It's my first diy chassis, the blank top plate was scored cheap from a local engineering supply co & the wood was a scrap lot off the bay. A good excuse to use the bench drill I bought a couple of years back.

Apart from the slight hum which you can't hear when a track is playing it sounds great. I will take the test voltages later today & post the results as I want to know why the bias meters are only reading 30ma.

Re the hum I think I either have a problem in a tube...(I've swapped em out/round with no change)....a wiring problem....I'm not 100% happy with the layout...a/c crossing in too many places ...need to see what I can do to tidy this up ...or a grounding issue.....I've grounded the centre tap & I will double check the soldering here & a safety earth to one leg of the power tx as standard....not sure what else to check here.

Mike
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Postby Thermion » Sun Feb 26, 2012 7:38 am

Mike, very nice job on the amp. The blue LED enhances the blue glow of the tubes and the blue Edcors.

My amp was dead quiet, so we should be able to help reduce yours. I agree that you have some signal wires crossing AC that could be problematic, but I think it is probably a wiring or grounding problem. In your picture of the underside, I see yellow wires from the output transformer secondary common terminal (white wire) connecting to terminal J10-1 and J11-1. It also looks like you do not have wires connected from the positive terminal (green wire) of the output transformer secondary to the board. Please check this. If I am correct you do not have your output grounded, and your NFB loop is not connected properly.

The correct connections for the output transformer secondary is to go from the common wire (white) to ground (J10-2 and J11-2) and from the positive (16 ohm) wire (green) to J10-1 and J11-1. So you need a pair of wires going from each speaker terminal pair to J10 or J11.

I suspect that if you move the yellow wires from J10-1 and J11-1 to J10-2 and J11-2 it will solve your hum problem. Then connect wires from the positive speaker terminals to J10-1 and J11-1 to complete the feedback loop.

If possible, a higher resolution picture of the underside will help diagnose any other problems.

I look forward to seeing your voltage measurements. It would be nice to know for sure what current is flowing through the tubes. I suspect that the meters may not be connected just right. Also, it would be nice to know what your B+ is. BTW, what power transformer are you using?

Hope this helps.

Cheers,
JT
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Postby Shannon Parks » Sun Feb 26, 2012 9:44 am

Looks great, Mike! Makes me eager to change my ULtra to 6BG6s today.

Definitely post your voltages - that can really help sometimes. What values (both the resistor and cap) did you end up using for the feedback circuit? Finally, some close up big photos would be great for troubleshooting the hum. You can mail the directly to me, too.

Shannon
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Postby whaam68 » Sun Feb 26, 2012 12:30 pm

Hi Guys
Hum solved! JT you were right I totally messed up the feedback connections by not reading your previous post closely enough...duh :$
Anyways now corrected & zero hum....well a tiny bit of mechanical hum from the dynakit PA power tx but you only hear it when your stood on top of it & the GSG uses the same tx & has it also. Brought it straight back in & cranked up the Velvet undergrounds Sister ray on the Matrix sampler & some Beth Orton. Now sounding much smoother & with that triode bloom and plenty of power.....very nice....pic "in action" attached

No voltages yet (I had to build a 15ohm dummy load first-now done) but I will get on it tomorrow night. Meters still reading low...I will try & add a better underside shot.

Shannon I used 1K in the feedback circuit and increased the cap value to 1000pf 63v polystyrene in paralell...is that ok? I assumed there was a relationship with the resistor value?

regards
Mike

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Postby Thermion » Sun Feb 26, 2012 2:04 pm

Mike,

Glad to help!! I love my 1625 Clementine Ultra. IMHO the 807/1625 is a sweet sounding tube. One of the best sounding tubes ever. I think you will really enjoy the new amp.

You are still an order of magnitude away from the recommended FB cap value. Shannon recommended a 6800 pf cap. (or .0068uf, 6.8 nF) 63 volts is fine, that's what I'm using. Shannon may weigh in with some additional advice. I wouldn't worry too much about it though if everything sounds OK.

I would still like to know your voltages. If you followed mine and Shannon's cathode resistors, then you should be close to 50ma on the 807's. It may be that the meters are affecting the circuit.

Those Wharfdales look cool. I bet they sound great too. I picked up a pair of B&W 802 Series 80 speakers about this time last year. They kick ass. British speakers rock! I was at a conference in June in Bath and went to an audio store that featured B&W speakers. I listened to the current 802's and a pair of 801's in piano lacquer. I asked the guy how much for the pair of 801's. He said, "they are 18 and a half thousand." I said, "dollars or pounds." He said, "Pounds." At that point I shook his hand and left the store.

Cheers,
JT
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Postby whaam68 » Sun Feb 26, 2012 2:40 pm

Hi
well I appreciate the time! I will dbl check the bias resistor value tomorrow with voltages after I get back from work and I can parallel another cap if needed.
British speakers do rock....I'm partial to the vintage stuff, those were £20 and they had been re foamed by a pro and french polished to boot...seller preferred his lowthers. I have a bigger set upstairs with 15" woofers....more 60's wharfedales that look like laundry baskets but sound really good. I really regret selling my original leak sandwiches but the house is pretty small :( All the vintage 15ohm stuff is easy to drive so great for tubes (or valves to us Brits).
I have most of gilbert Briggs books...really ahead of his time...Bath is a very nice town ....very posh...probably why they wanted 18k for speakers (sick)
Regards
mike
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Postby Shannon Parks » Sun Feb 26, 2012 5:41 pm

whaam68 wrote:Shannon I used 1K in the feedback circuit and increased the cap value to 1000pf 63v polystyrene in parallel...is that ok? I assumed there was a relationship with the resistor value?


I think you are probably OK with the 1000pF cap. Your resistor is approximately 1.414 larger and is correct for 6dB of feedback, like Thermion's and mine. I used a 6800pF cap, as I have a box of'em, though I could have used a 4700pF if I had one. So dividing that by 1.414, we get a 3300pF or 3.3nF cap. This is a more optimized value, but probably not really needed, as we aren't too worried about stability.

Listening to my one hour old 6BG6G Clem ULtra right now, btw, with my almost 1yo daughter. I'm not sure Ummagumma is her cup of tea, though I promised several species of small furry animals were on the album. [:)

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Postby Ty_Bower » Sun Feb 26, 2012 5:54 pm

separks wrote:I'm not sure Ummagumma is her cup of tea, though I promised several species of small furry animals were on the album.


Don't worry, my 10 yo daughter still doesn't quite fully appreciate why the track is titled "Sheep", even though I made her listen quite carefully at the end. What can I say? She's the one who picked it.

They'll get it eventually.
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voltages!!!

Postby whaam68 » Tue Feb 28, 2012 2:00 pm

Hi All
After getting distracted with the girlfriends broken down car last night (major pain) I have gotten time to do this.

V1 6SL7
Pin
1 0v
2 201v
3 1.7v
4 -0.9v
5 201v
6 1.7v
7 312v
8 314v

807

1 N/A
2 3.15/3.12v
3 N/A
4 384/384v
5 0v/0v
6 N/A
7 3.1/3.1v
8 34/33v

I didn't do the plate cap!!!!!

J1.1/1.2 0v
J2.1/2.2 0v

J3.1/3.2 380v/380v

J5.1/5.3 319/319v
J6.1/J6.2 400/405v

J7.1/7.2 387/387v

J8.1/8.2 3.14v

Mains voltages may be down a bit as my "workshop" is down the bottom of the garden with a long cable run from the house?

So does this look right? What's my bias? & are my meters reading right at 30ma?

regards

Mike
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Postby whaam68 » Tue Feb 28, 2012 2:02 pm

oh & to clarify I've taken the 807 readings from the 6L6 pinout numbers on the board!!!! (not the 807 pinout #'s which are quite different).

Cathode resistors are R17/20 1.2k 3w
R18/19 1.5k 3w
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Postby Thermion » Sat Mar 03, 2012 7:44 am

Cheers Mike,

I know what you mean about girlfriends cars. Been there, done that.

Sorry for the late reply, I was on a business trip all week. Your voltages all look good. I assume that on pins 7-8 of the 6SL7 you meant 3.12 and 3.14 instead of 312 and 314. These are the filaments. A concern is the -0.9v on pin 4 of the 6SL7. This should be very close to 0 like pin 1. Did you have the inputs shorted when you took the measurements? You may want to double check this measurement just to make sure nothing is wrong. It could be something in the volume control wiring.

The 1.5k and 1.2k parallel pair of cathode resistors give you the evil value of 666.66 ohms.(666) You measured 34 volts on pin 8 which gives a current of around 51 ma through the 807s.

So, there is still the mystery as to why the current meters read 30ma instead of 50ma. How do you have them connected? Is it possible they are only reading the current through one of the cathode resistors? It would help to have a photo of the connection of the meters to the cathode resistors.

Regards,
JT
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Postby whaam68 » Sat Mar 03, 2012 9:45 am

Hi JT

Hope you had a good trip!
I will re check the voltages. Inputs weren't shorted & the vol pot isn't connected yet...I always leave this until I get everything else working right!

I've done a close up....blue wire to -'ve of 100ma meter....let me know what I've done wrong ;)

regards

Mike

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Postby Thermion » Sat Mar 03, 2012 10:38 am

Hey Mike, thanks for the picture. I see what's going on.

The cathode resistors need to be to be treated as a pair. Whatever you do to one, you have to do to both. They act as a single cathode resistor. Shannon did this so you can use a pair of 3 watt resistors in high dissipation designs instead of a very large 5 or 10 watt single resistor.

So by pulling one of these off the board and wiring it in series with your current meter, you are only measuring the current through that particular resistor instead of the pair. The current is divided between the two based on their resistance value. With 51 ma through the pair, the 1.5 k resistor will have 22.67 ma and the 1.2k resistor will have 28.33 ma. You are measuring the current through the 1.2 k resistor.

So if you want to have the meters measuring the total current through the 807, you will have to remove the other cathode resistor and solder it in parallel with the one on the meter.

Hope this makes sense.

JT
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