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Hi All
After a 2 year layoff due to some health issues (major PE) I've finally blown the cobwebs off the soldering iron & am building a clementine with some of my stash of 807's. Board is now stuffed using Shannon's "ultra" post notes & I'm very curious to see how this one works out compared to my GetSetGo (which is an awesome sounding amp). I knocked up the chassis out of some hardwood planks off ebay & won't be winning prizes for joinery! but it will do. Next step is drilling the top plate & mounting the transformers. I had to order a bigger punch for the 807 sockets grrrr which is on the way...I will mount these on the top plate & run wiring to the sockets.

I've always wanted an amp with bias indicators, anyone know if 100ma dials will do the job & how I go about connecting these up to the board? (yes I am that stupid!)

Updates & more questions as I go!

Mike

Very cool, Mike. Don't hesitate to ask. I'm so fond of the 807/1625 tubes, and I'm glad to see you are trying the Ultra version.

Shannon

100 mA meters should be good, the expected currents would be between 60 and 80 mA, max.

It would be best to connect them in series between the bottom of the cathode resistor(s) and power/signal ground, that keeps any high voltages off them, and they will be very close to zero volts potential in reference to the DC power and signal grounding.

Just lift the "ground" end of the two cathode resistors for each V2 and V3 807s, and then conenct the meter's positive terminal to the "lifted" end of the resistors, and the negative terminal to the original ground pads.

HTH

/ed B in NC, USA

Cool....IWill get drilling at the weekend
Thanks for the steer.

Mike, this looks like a great project. I built a similar amp using the 1625 which is a 12 volt equivalent to the 807. I also used tube sockets separate from the board. See my posts for pictures and measurements.

I have my tubes biased at 52 ma, so your meters should be just right. I've been listening to my amp for about 6 weeks now and really like it. Let me know if you have any questions.

JT

That red and green!

Rockin', dude!

OK Some progress on the build.....most of the metal bashing done though mighty cold in the tool shed at -6deg C. Still waiting for the chassis punch for the 807's.....starting to look like an amp....boy this hardwood is a little thick....tricky to cut through!

Still debating about a volume pot....anyone know what value is suitable? & also I found a really neat sub miniature DPDT toggle switch. It's rated 2A at 250v A/C & 5A at 30v DC....is this ok to use or stick with my usual "big switches"?

Mike

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Hi
This build is 3/4 done and I'm wiring up now. Having re read Shannon's ultra notes I'm confused on the opt connections.....I'm using GXSE 15 16 5k for my 15 ohm speakers....wiring is
Blue plate
White/blue screen
Red b+

Green 16 ohms 2ndry
White common 2ndry

Looking at the note

B+ to j71 and 2 as standard 6L6
Screen to J3-2 and J4-2
Plate still to j3-1 and J4-1?
Then it seems to say 16 ohm 2ndry to J10-1 and J11-1
And 2ndry common to j10-2 and j11-2

Im being thick here but what's connected to the speaker terminals?
I would really appreciate a steer.
Thanks
Mike

Hi
This build is 3/4 done and I'm wiring up now. Having re read Shannon's ultra notes I'm confused on the opt connections.....I'm using GXSE 15 16 5k for my 15 ohm speakers....wiring is
Blue plate
White/blue screen
Red b+

Green 16 ohms 2ndry
White common 2ndry

Looking at the note

B+ to j71 and 2 as standard 6L6
Screen to J3-2 and J4-2
Plate still to j3-1 and J4-1?
Then it seems to say 16 ohm 2ndry to J10-1 and J11-1
And 2ndry common to j10-2 and j11-2

Im being thick here but what's connected to the speaker terminals?
I would really appreciate a steer.
Thanks
Mike

Hey Mike, Looks like you are making good progress. You are on the right track with your connections.

B+ to J7 1 and 2.

Take the Screen directly to your 807 tube socket. If you already soldered a lead from the tube socket on the board to the 807 socket then go to J3-2 and J4-2 as indicated.

For the plate, I pushed the output transformer cable through a hole in the chassis and soldered my plate cap directly to the lead. So the blue plate wire goes directly to the top of the tube.

For the secondary, I soldered the outputs ( in my case 8 ohm) to the speaker terminals and then ran a wire from the negative post to ground (J10-2 and J11-2) and a wire from the positive post (16 ohm) to J10-1 and J11-1. This completes the feedback loop.

Here is a picture of the underside of my amp. Unfortunately I hadn't run the feedback lines yet when I took the picture, but you can see how I did the tube socket connections. ( I used a 1625 instead of 807 though)
http://www.diytube.com/phpBB2/album_pic.php?pic_id=148

You will also need to change the value of your feedback resistor from Shannon's recommendation since you are using a 16 ohm output. You may have to tweak this somewhat to get the feedback to the level you want.

JT

Cheers JT much appreciated. I haven't yet soldered the 807's as the eBay vendors 1 3/4 socket punch went AWOL so I'm
Waiting on the replacement I ordered. Virtually everything else apart from the final hookups is done. I've soldered long wires from the 6L6 sockets on the board in readiness so I Can do the hookup straight to the plate cap on the tube.

I was wondering if I would have to change any values for my speakers
the feedback resistors are r27 and r 28 right? I have used 2 .1 k paralleled with some silver mica caps salvaged off an old heathkit chassis. Any ideas of ballpark values to try and can I parallel another value underneath to save keep desoldering the board?

Regards
Mike

Errrrr scratch that I actually used 680r for r27 and 28 per the note not the 2.1 k on the diagram.....

Mike, R27 and R28 are the feedback resistors. I used 681 ohm resistors in my amp per Shannon's recommendation. We were prototyping circuits at the same time and comparing results. His with 6L6 and mine with 1625. I used a pot for my feedback resistor and did power and THD measurements for 0, -3, and -6 db of FB. Unfortunately, I didn't measure the pot resistance when I was doing this. My Bad!!! So, when I built my amp I used Shannon's 681 ohm value for my feedback resistor. This was bypassed with a WIMA 6800uF/63v polypropylene film cap. My output transformer was an Edcor GXSE15-8-5K.

Since your are using an Edcor GXSE-15-16-5k, you would need to increase the resistance value by SQRT of 2. So 681*1.414=963 ohm. This is due to the turns ratio difference between the two output transformers.

When I measured the performance of my 1625 amp, the 681 ohm feedback resistor resulted in 8.3 db of negative feedback. This was more then my target of 6 db.

So my advice would be to replace your 681 FB resistors with 1K or slightly greater resistors. For this amp anything between 6 and 9 db of feedback in UL mode with an 807/1625 should give very good results. The tradeoff is gain versus THD. If you are planning to use a preamp or line level source with this amp you will be OK. If your want to use a mp3 or phone, then you will want to reduce the feedback to increase overall gain.

JT

OK will do I will go with 1 or 1.2K ish & see how that works. I don't really need big gain as my speakers are all big (ish) vintage 15ohm 50's/60's wharfedales & very sensitive. GSG goes loud. I'm using a Yaoin MS12B active preamp with a level pot so no problem with driving. Can I just check the cap value as the notes suggested .0068uf or 680pf which is what I used?
regards
Mike

The cap value is 0.0068uf or 6800pf. I had it wrong in my previous post.

JT