Why does my Elk amp sound like a dishwasher?

[poweredbypoptarts]

I was Google searching for more info on this amp and discovered an older thread here on the forum! Funny thing... I couldn't find the thread when I searched the forum with its own search function! It just goes to show how important it is to get the right search terms. And, what do you call the phenomena of clicking from one link to another to another until you arrive at a site you want but now can't remember how you got there? Yeah, that happens a lot to me?

Anyway, here is a link to an older thread here on this very forum about this amp.

elk amp 50 with matching 2x12 cab

-=- Boris

[poweredbypoptarts]

Here's an update. I have been slowly (and I mean slowly) working on cleaning up some of the wiring in this amp. Most of my time spent on this amp has gone to tracing lines and components. I poke and prod with my little wood stick lots. Then, I warm up the soldering iron and get to work. There are rigid connections on both long sides of the board to components like tube sockets and potentiometers that prevent me from lifting the board and gently flipping it over. Most of these connections are for GND. I have one more connection to move and then I will have easy access to the caps hidden on the underside. My plan is to move the caps to the top side so there will never be a need to flip the board in the future. That could make it crowded up top but I'm going to try to keep it tidy. Keeping the freshly redirected GND lines tidy is a challenge. It would be real easy to simply unwind a spool of wire inside this chassis but that would be a disgrace!

The hiss has gotten noticeably quieter since i shortened the GND lines. I didn't take a sound pressure level reading along the way but now I wish I did. Oh well...

I have continued to update the schematic with some additional notation. A copy is attached here. I welcome any comments you may have.

-=- Boris

elk es30 schem with notes 2012 11 17.pdf

[paggerman]

Hello everyone,

My name is Boris and this is my first post to the forum.

I recently bought an Elk Custom Amp 30 with a 2x10" speaker cabinet. The amp sounds great and I love the vintage tone. I know these amps are Fender-ish clones in appearance but have their own unique circuit design. My only problem with this amp is all the background noise it has. It sounds like a dishwasher or a record player that has reached the end of the record. Adjusting any of the knobs does not affect the warbly background noise. The noise is always there.

I think my only solution is to slowly rebuild the amp. Some of the caps have seemingly been replaced by the previous owner (or maybe even the owner before him?) but not all of them. Most of the old wire wound resistors are still in place (95%+) but I read that their values can drift over time as the wire undergoes heat stresses and ages. I tried to find a schematic and all I can find is one that is labeled Elk ES-30. This schematic seems to be the right one but I haven't compared 100% of the circuitry against it. A copy is attached to this post. The schematic shows two 7189 power tubes but I have two EL84 tubes. I read that the 7189 tubes are similar to the EL84 tubes but the 7189 tube run a bit hotter. The EL84 tubes look new with fresh silkscreening but the other tubes look older.

I'd like to rebuild this amp in a logical order. First, I would like to get rid of the warbly hiss. What should I attack first? Should I replace the rest of the caps? Should I get real 7189 tubes? Second, I'd like to restore the amp to the right components. What I mean is that the previous owner messed with some parts of the circuit. Some resistors were changed. Where he didn't have the exact value he would take two and tie them in parallel (i.e. needed a 12k so he tied two 28k units in parallel to get 14k, a close value, etc). I was planning to go through the schematic and make a bill of materials so I can order all the replacement resistors in one swoop from a place like Digi-Key. What power rating should I get? Should I get 1/2W resistors? Third, what does "(2L)" next to a resistor value mean? Was that the Japanese way to say 2 Watts?

Thanks!!!

-=- Boris


[ATTACH=CONFIG]20793[/ATTACH]

Hi Boris. I recently posted with a very similar problem - indeed I described the problem as sounding like the run off groove of a vinyl record. I had tried all sorts of things with no improvement. Turns out that the pre-amp valve (a NOS Russian 6n2p) was dodgy. Replaced it with a 6n2p-ev and all the noise went away (apart from my guitar playing).

Good luck with your build.

[dai h.]

what Dave describes about the Rs appears correct (ceramic tube w/carbon track on it). They are "Type L" resistors which apparently used to be common. I see them in surplus very occasionally. The guess about the number equalling the wattage rating also looks correct ("1L" = type L 1watt, "2L = type L 2W, etc.). This file shows some of the physical sizes of type L, (also older) type P, and modern RN and RS in a side by side comparison (may have to dwnld. Japanese font??) :

http://www4.tokai.or.jp/radioshack/p...en_and_now.pdf

also, read (on a japanese site) that the lead to carbon track connection can go open in these Rs, so might be better to preempt failure and just replace them. Additionally, (from my experience w/the caps) I would just replace any old Japanese oil caps w/"CP", or "CP-C" (usually grey or blue) which have DC on them since they seem to always leak (or end up doing so). (I do however have some older looking Matsushitas which seem okay though. If you REALLLY have to have oil for whatever reason, I would suggest trying American hermetically sealed types since they seem to be good--IIRC did have a old Sangamo and some British oil that seemed leaky or bad though.) Also, I would check old micas (maybe in a red bakelike-looking package) for leakage and replace as necessary.

[poweredbypoptarts]

dai.h,

Thanks for the confirmation and the PDF. I was able to open the file and see it. The leads on some of my resistors are starting to fatigue and I want to replace them. I think it is because the resistor was mounted in such a way so the markings are blocked. So what did all the previous owners and myself do? We twist and rock the resistor to see the values.

All I managed to do today was replace a cathode capacitor on the first 12AX7 preamp stage. It is not shown on the original schematic. The original cap was a 50uF, 15V unit. That cap was dried out and registered only a few nF on my meter. I replaced it with a 25uF, 50V unit. Wow, what a difference that made!! I read that it increases gain and I can definitely hear it. Humbucker equipped guitars need the volume rolled back but my Strat just sings through it!

-- Boris

[dai h.]

yeah, that would definitely reduce gain if the cathode bypass cap was completely dried out. Glad it's working better for you!

[poweredbypoptarts]

I wanted to post an update on my progress in restoring my Elk Custom Amp 30. A lot of my time has been spent moving capacitors from under the board to the top. This not only allows me to see what their age and electrical values are but to also make it easier to trace the circuit and service the capacitors in the future. The circuit looks a lot more "busy" now. I really wish I had reference designators! Since I have been working with the amp for a while I am familiar with the location of the components so I am not getting lost. I have four more capacitors to move up on top.

I have also been replacing whatever old capacitors I found with new electrolytic and ceramic units where it makes sense. Some of the installed capacitors look fairly new so I am not replacing those.

As I work on the capacitors I compared the as-built (or as-found) design with the schematic and make changes. Sometimes I adjust the amp but most of the time I adjust the schematic.

I also swapped out the first 12AX7 tube in the signal path with a new unit. The "old" tube was a fairly new-looking Electro Harmonix 12AX7EH. It has a date stamp of "05 12". I'm not sure if that is YY MM or MM YY. The new tube is also an Electro Harmonix 12AX7EH unit and it's date stamp is "12 05". Yes, the numbers are flipped! Coincidence? Probably. Anyways, I replaced this tube because it seemed microphonic. When I tapped it with a wooden probing stick I could hear the taps on the output of the amp. However, my new tube is even more microphonic. When I tap it with my wooden probing stick the tube makes a sound similar to whistle whose volume quickly tapers off. Just imagine the acoustics of dropping something off a cliff minus the doppler effect. My amp is on its side so I don't know if the orientation of the tube is the cause of the microphonic quality.

That said, replacing that first tube in the signal path eliminated what feels like 95% of the whoosh, hiss, and flutter! My amp is nearly whisper quiet when it's idling. I do hear a tiny bit of 60 Hz hum but it's very small. Miniscule.

Changing the tube improved the tone a lot! My single coil Strat has a much more glassy and well defined clean tone. It definitely has a jingly bell-like tone. I can hear the pick run over the strings now. It sounds really great to me!

I have plenty more work to do in addition to moving the remaining four capacitors to the top. First, there are other tubes to swap out and experiment with. Second, the power output stage has EL84 tubes instead of EL84M. Third, I want to restore the bias circuit to the original design. Fourth, I want to clean up some of the wiring around the transformer and rectifier caps. The wires are pretty long with a lot of slack in them.

I am attaching a PDF copy of my modified schematic along with my notes as it stands today.

Thanks!

-=- Boris