The Amp Garage

Sounds interesting. Make sure it's not too noisy, though. SMPS are very noisy. Also, how do you plan to have your filaments powered? Use the same DC power section (before it is raised by switched mode for HT) or use a separate 12VDC? The Eddy Van Halen trick might be good too. Ideally, it should low...

If you take the voltages posted above, the idle current drawn by the output PP is about 20mA. Each triode in the preamp can be reckoned at about 1mA. So that's 24 or 25 mA for idle. Don't know about peak. It probably doesn't change much for the preamp section and might increase a bit for the output ...

What schematic did you use? Matec's HTM1?
May be it is the 150V HT that is too low. What is your DC voltage at the power stage?

Have a look at the voltages on the attached picture. This will give you an idea.

Nice build

How does it sound? Do you have PCB layout?
What TR did you use? I can see a small Hammond for output, but what is the power transformer?

Hi everyone, Odrpol, your output tube V3 draws too much current, about 20 mA per triode and that is way too much for 12AU7. Calculated dissipation for each triode is about 5 watts, but it should not go over 2.5 W. If you want more output power, use ECC99 instead. It's a good replacement tube for 12A...

Yes, you are right. I knew I was wrong at the minute I posted this. A 30V drop with about 30 mA per leg would make a 1k difference in DC resistance. That's definitely too high.

Too bad for the iron.

About the connection of OT transformer – I have read in the datasheet of 12AU7, that the maximum rating of anode voltage is 300 V, at main 294 V I’m afraid that is to nearest from maximum, following datasheet, and I connect the OT to lower tension to get about 250V at the anode this valve. At datas...

Oh I see now. Sorry about the mismatched tubes. I was wrong. If you always get the same unbalanced voltages always lower on the same side, that probably means your OT is part of the problem, if any. What I mean by "if any" is that it may be due to a difference in DC resistance between both primary w...

Hi there, Yes, as Matec said, something is definitely wrong about your measured voltages. Aso, you should stick to Matec's original schematic or even use his HTM1 schematic which has best of both worlds. The way your output transformer center tap is connected to a lower B+ is not correct to me. :roll:

Different plate voltages just mean output tubes are not matched perfectly, but that should not prevent the amp from working.

As for the popping noise when you smack your amp, may be preamp tubes become more microphonic when they heat up?

I quickly re-read this topic and, maybe I have missed something, but it seems that you have put back two new caps without removing both straps where the diode bridge used to be, and without installing a new bridge. If so, you are filtering 6.3 VAC without first rectifying it, and that's not good at ...

At first glance, it seems that previous owner or someone else has removed the DC filtering part for preamp heaters and chose to power all heaters (preamp and output) with AC right from the PT secondary. That's why the diode bridge and both filtering caps C122 and C123 have been removed. Now, why did...

Hey Matec,

Check you PM mail, there's a cool pdf file.

Hi, This is my first post here, though I've been following and reading a lot about JTM1 and other builds for some time. Littlewyan, why not have a look at this OT from OEP: http://www.oep.co.uk/pdf/N35A002F%20issue%205.pdf It is sold for about 15 quid VAT and shipping included in UK. You can find it...