trinityamps.com

Keep us posted on your tonal experiments with the different tubes.

_________________
Great tones come in small glass jars!

Sure will! It's a waiting game now for the tubes to get here.

I'm also going to be testing a bunch of pickups in my Explorer and then will be auditioning a new 12" speaker in place of the Greenback in the Night Train cab I'm using.


So far if I feel like getting crunchy and gritty right away, its a Sovtek 6V6. If I want a bit more room, its a Groove Tube (Ampeg branded) 6L6.

Updated picture, classy little Tramp in all her glory!


The first bypass resistor appears to be getting cooked... didn't notice until I shrunk these pics but I took a peek and sure enough it's well done. Any suggestions or tips on why this is happening or what I should look for to cure it?


More pics here if anyone wants to see. Sorry for the watermark but I'm using the same pics on some other forums where I pedal my wares (bad pun)!
http://www.stuntmonkeypedals.com/pics/o ... amp/02.jpg
http://www.stuntmonkeypedals.com/pics/o ... amp/03.jpg
http://www.stuntmonkeypedals.com/pics/o ... amp/04.jpg
http://www.stuntmonkeypedals.com/pics/o ... amp/06.jpg
http://www.stuntmonkeypedals.com/pics/o ... amp/07.jpg

Those resistors are bleeder resistors across the filter caps to drain the high voltage when the amp is shut down.

Those first two caps have up to 410V DC on them. One has 410V on it all the time and the other has a varying voltage up to 410V based on how the VRM is set.

P = V^2/R
So we got P = (410V)(410V)/220000 = 0.76W

Your poor little resistors there are only rated for 0.5W. They can't handle the extra 0.26W and as a result are burning up. (The resistor beside the burnt one will burn up at any time btw).

The original builder didn't use the supplied metal oxide 220K 2W resistors he should have. Those 1/2W metal film resistors are meant for the plate position not the power supply.

_________________
http://pdfelectronics.com

Thanks for the quick reply! I have to accept full responsibility for those resistors being there; on reception they were all in a little baggie and completely untouched. I assumed they were a later version addition that he just didn't add and I put them in based on the latest schem and also assumed they were the 2W resistors. Will have to replace them asap, but in case of failure, it shouldn't hurt anything and only leave the caps charged up when powered off correct? Can they catch fire if they fail? I've blown up some IC's and burnt up some LEDs but have yet to have a resistor go.

On a side note I received a batch of KT88's and they are absolutely gorgeous on this amp! I thought the 6V6 and 6L6 sounded good but the Sovtek KT88's are so sweet and buttery. I may not go back!!

They shouldn't catch fire, just a quick poof of smoke and some bad smell.

Remove them for now. Make sure when you install the new resistors the caps are drained of their high voltage.

_________________
http://pdfelectronics.com

KT88 - I have NOS Tung Sol. Agree on the tone. Very sweet.
Layout shows 2W for those resistrs I believe. Get some metasl oxide 2W,but you can live without them.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I have some proper resistors on the way and a new .01 cap to replace the one I broke and replaced with the .022 Orange Drop. I pulled the chassis out of the head and wouldn't you know it started acting up again! I was getting a bunch of frizzy sound, cracking and popping and volume spikes and dips. It didn't make a difference which pot I turned, it was a full on static mess!

I flipped her over and nothing stood out aside from the browned resistors so I started poking around again with a small paintbrush. Once more I found my issue on the volume pot but was able to isolate the shielded wire coming from the pot to the 330k (12AX7, pin 7). I found that tapping the wire close to the pot added some hum and tapping/tugging it close to the resistor made everything go really bad. I pulled it out and replaced the entire thing with some shielded guitar cable and so far it seems to have done the trick... again. It's big and ugly but is holding tight and no matter how I manipulate it the sound remains consistent. The amp has a lot more range in the controls than before, the 'Tude gain is amazing and overall volume is a lot higher than it was.

I haven't looked closely at the offending wire, but I'm thinking it might have a short on the tapered end where the shrink tubing was applied. Pushing on that spot when it was in the amp gave the clearest change in performance... I also had a smaller piece of shielded wire that won't fit anywhere so I think the longer piece I pulled out may have been the issue with the amp for the first builder. I just got lucky for a while and must have had it placed just right to not short out. At least that's what I'm hoping as it's once again working as it should!

The sound is now consistent and as I said, much LOUDer! No more crackles at all but now I have a buzz that shows up when I turn the Master Volume anywhere from 6 - 10 but goes mostly away at full volume. It also dissipated but is still preset with the Power turned down to 6. With the Power on 6 and the Master Volume on 11, it's less noticeable but dropping the MV down from max even a hair and the buzz/hum comes back pretty hard.

I've tried poking wires and moving things around, also tried changing tubes and all the different settings on the impedance selector but nothing changes it except sweeping the pots. I've also tried a different speaker but it's the same... It's also nothing on the input as the buzz remains with no cable plugged in.

Edit: It's not shown on the schematic, but I went through the build docs again and noticed on page 39 the pic shows a shielded cable from Master Vol to pin 6 of the socket. I replaced the wire I used with some shielded wire and it's now quiet.... well, there's a bit of hum when I'm seated about a foot from the speaker right at ear level, but I suppose that's to be expected

You mean MV wiper to the 330K resistor that is then going to pin 7. Correct

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yes, that's the one! Happy to say I can get to my tube rolling now; I played the amp for a few hours last night just to see if anything else would arise and it's back in fighting form. I think the additional hum must have been there but only started showing up when the other shielded wire was replaced and that side of the amp was working right.