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Title: Finished my build! Post by: Tahoebrian5 on February 12, 2012, 06:27:00 PM Fired my hrm50 up for the first time and everything is working just fine. A bit bummed that my power tubes are not matched well.. Like 3mv off.
Anyway I dialed in a really nice British crunch on the od channel. I am having trouble getting the smooth blues lead sound I've come to expect based on sound clips though. Probly needs to burn in a bit. Also I'm using a genz Benz 2x12 cab for now. All in all I'm very excited to learn how to dial this thing in! Title: Re: Finished my build! Post by: wyatt on February 12, 2012, 09:37:32 PM Typically within 5mA is considered "matched" for 6L6GC, EL34 and other large octals.
Smaller wattage tubes, like 6V6GT or EL84, need to be within 3mA. Title: Re: Finished my build! Post by: mcinku on February 12, 2012, 09:38:55 PM Nothing better than playing the amp you built for yourself.
Don't worry about 3mV difference... the amp will sound just as good. Enjoy it. ;) Title: Re: Finished my build! Post by: SoundPerf on February 13, 2012, 12:13:58 AM Yeah, 3mV should be fine. That's what mine are right now. I think a little imbalance is actually not such a bad thing with these amps.
Burning in will help for sure, also with the HRM I find dialing the gains back some will help get you to the Dumble tones. Keep the back panel OD trim to around 11:00 and mess with the internal OD trim too. I tend to keep the preamp level around 6 or 7 and back off the OD drive to (4 to 6). I'm using a C/D-lator so I put the OD Level about 4 or 5. This is in the Rock voice and PAB on. You'll get there in time. Title: Re: Finished my build! Post by: Tahoebrian5 on February 13, 2012, 03:08:15 AM So, I've checked the PI trim pot today and it seems something is off. I'm getting a difference in voltage of around 180 volts instead of 6. Ive tried the full range of the trim pot and it really has not much affect. So the closest I've been able to get is V3a=257v V3b=436 volts. I've got a question emailed to Nik but thought I'd see if any of you experts have any suggestions. It does seem like the amp has a really lot of pop.. almost like a telecaster tone.
Title: Re: Finished my build! Post by: Tahoebrian5 on February 13, 2012, 03:18:49 AM Did some more poking around. The voltages on the actual pins of the trim pot I have even, but when you get to the other side of the 100k & 110k resistors the V3a voltage drops drastically.
Title: Re: Finished my build! Post by: 212Mavguy on February 13, 2012, 03:20:26 AM Just now I saw the latest post from the OP, so take my words with a big-assed shovel of salt...but once you get your PI "sitchiation" taken care of...
IMHO, +1 on the imbalance thang. 3-5mv not a biggie. When I had my 50w HRM built I asked Nik to set the PI trimmer for a PI tube having matched triodes at time of build. I never have touched it nor have I fiddled with the HRM tonestack. Being an OCD-ish tube collector, I have a fave pair of 6bg6ga Sylvania grayplates (repinned 7581a's with a plate cap) in adapters, also 3mv apart. I swapped those back and forth in the tube sockets and in my case my amp sounded best with the tube drawing less current closest to the PI. You might try that and see if you can hear any difference, in my case I could as far as sustain/bloom was concerned. One way or the other... Congratulations on your build, my hat is off to you, and to all those who built their own D-clone(s)! Title: Re: Finished my build! Post by: SoundPerf on February 13, 2012, 05:31:58 AM Read through this thread. It's long and goes round and round a bit. But there's a bunch of good info about the whole PI thing. Even though I'm fortunate enough to have a scope, it's not a necessary. But getting just what points you should be measuring is the part that seems to get people confused. I still have to make sure I'm doing it right if I haven't done it for a while. Also, wants you get it close, it's best to just use your ears and follow the suggestions about that.
http://ampgarage.com/forum/viewtopic.php?t=13993&start=0&postdays=0&postorder=asc&highlight=&sid=431f2ea81eb16434a3b188af9f1d04af (http://ampgarage.com/forum/viewtopic.php?t=13993&start=0&postdays=0&postorder=asc&highlight=&sid=431f2ea81eb16434a3b188af9f1d04af) Title: Re: Finished my build! Post by: mcinku on February 13, 2012, 07:04:55 AM So, I've checked the PI trim pot today and it seems something is off. I'm getting a difference in voltage of around 180 volts instead of 6. Ive tried the full range of the trim pot and it really has not much affect. So the closest I've been able to get is V3a=257v V3b=436 volts. I've got a question emailed to Nik but thought I'd see if any of you experts have any suggestions. It does seem like the amp has a really lot of pop.. almost like a telecaster tone. When setting PI balance you should be measuring AC voltage and not DC. If you have a scope connect probes to plates, set the scope to measure AC, then use "sum" function. The goal is to have set both Vpp at the same value. Here's the video I made a while back... http://www.youtube.com/watch?v=8lNuu7TzzNU (http://www.youtube.com/watch?v=8lNuu7TzzNU) Title: Re: Finished my build! Post by: Tahoebrian5 on February 14, 2012, 05:14:35 AM Ok, go the problem figured out. The link that ties V3 pins 3 & 8 were missing a solder joint. Thanks for the input
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