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Vertical 6EM7 Portable Amp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5134
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Author:  john55 [ 11 Aug 2016, 10:31 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Hi,
Thanks for your offer of help. Here are some photos. If you need anything more specific I'll try and get close ups.
I've checked against the schematic again and everything seems correct.
I'm going to check the pin voltages now and will post the results as soon as I can.
Just a note: The speakers are connected with banana plugs. Pushing them in and out doesn't make the slightest noise through the speakers. I thought I should at least get a crackle?

Author:  john55 [ 11 Aug 2016, 11:27 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Voltages on 6EM7 valve base pins are as follows....
1....0V referenced to ground.
2....230V "
3....30V "
4....0V "
5....135V "
6....1.8V "
7&8.... 5.8VAC BETWEEN PINS and 2.9VAC FROM INDIVIDUAL PINS TO GROUND.

Author:  wdecho [ 12 Aug 2016, 07:42 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

A measurement from pins 3 and 2 would be helpful as well. I hope Matt responds to this post soon since no one knows the circuit better than him. I am not so sure about the 3 pin 30V but other than that the voltages appear to be correct. You are probably going to need to change the black and red RCA input wires on the pot. The way they are wired now is going to make them work in reverse. Closed is going to be wide open. The center pin of the pot goes to the #4 pin. I see at one point you are using the ground lug on one of the terminal strips. I never use it for anything. I accidently used it once when knowing better and sent my input signal to ground and had the same problem you are having. The one thing I am failing to see is how you have the OPT's wired.

A very nice looking neat build. This is part of the fun of diy, finding the problem and solving it yourself. I know it does not seem that way right now but the solution is there somewhere.

Author:  wdecho [ 12 Aug 2016, 08:03 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Ok, I notice on pin 5 you do not have the coupling cap wire correctly. The coupling cap goes to the #5 pin of the tube not where you have it. Change and let us know.

Author:  john55 [ 12 Aug 2016, 10:34 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Everything working perfectly. These two coupling caps were the last components fitted as I had initially ordered them incorrectly. The excitement of being able to finish the amp must have been too much for me. At first I still couldn't see it after you'd pointed it out.
I'll change the wiring on the pots tomorrow as I'm too busy listening at the moment. I'll also take your advice about ground lugs.
Thanks for your time and knowledge.

Author:  wdecho [ 12 Aug 2016, 12:09 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

I was just the first to notice it. There are many more knowledgeable members that would have seen the problem as well I just happened to be an early riser and was the first to look at the pictures.

Great looking build. Sound impressions later after you get some hours on the tubes. Matt is going to be proud when he sees the picture.

Author:  Suncalc [ 13 Aug 2016, 07:58 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

John;

The amp looks great.

However, I am a little concerned about the power sizing on some of your resistors. But I have to admit I'm having trouble figuring out exactly at what I'm looking. Are the silver caps next to the 6EM7 sockets your power stage cathode bypass caps? And are the two series resistors on them your power stage cathode bias?

Could you post a schematic showing the exact components you used and the power ratings on the resistors?

Author:  john55 [ 13 Aug 2016, 09:48 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Hi Matt,
These resistors were all bought as 0.5W metal foil. As you can see I've put a couple in series and a couple in parallel where I didn't have the correct values using one component.

Author:  Suncalc [ 14 Aug 2016, 11:12 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

OK. I see now that the silver caps are a bypass on the signal stage and the two resistors in series are the signal stage cathode bypass. This would make the black camps on end, the power stage bypass, correct. And the power stage cathode is connected to the red load resistors at the meters by the brown wire? I was having trouble following all the wiring in the pictures. I originally thought that the silver caps were the power stage bypass. My mistake.

The amp has a greta look. Is that real leather on the face? It looks great.

Author:  john55 [ 14 Aug 2016, 12:08 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

My component placing around the valve bases could have been better. I ended up having to sleeve a lot of component leads. In retrospect I would have preferred to use paxolin board and turret lugs. Yes, the load resistors ended up on the ammeter lugs as I was cluttered enough around the valve bases.
All six sides of the case are covered in top grain cowhide, glued stitched and dyed in situ. I'm a leatherworker by trade so not having the woodwork skills to make a case like yours it seemed the way to go.
I've been listening to the amp constantly for the past two days. I'm using some Mordaunt Short speakers that I've had for years and it sounds great. Crisp, clean and really good separation. At first I was a little unhappy with the bass, it sounded a little weak to my ears until I realized that what I was hearing was strong crisp notes as opposed to a deep booming noise that I had gotten used to over the years.
I really enjoyed building this amp internally and externally. I love the look of a your vertical amp and quite like the idea of building the "lacewood" as a vertical. Thanks again.

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