ELK viking 100

[DummyLoad]

picked this up off CL this past saturday. owner brought it to texas when he moved here from NY. 300 bux was probably too much, but i love old rare stuff so i stepped up. sounds really good, but tremelo is non-functional. the reverb sounds really nice and not too overbearing. the reverb tank is a custom part and will be difficult to source if it fails. i was hoping it worked so i guess i got lucky.
 

not much at all in cyberspace on this, seems like it's a spin of the elk twin-amp 50 as this one has the same tube line-up except has 2 OT, 4 x EL34 and SS rectifier.

has been worked on so don't know if what was done are mods or repairs: they seem to be repairs but i cannot confirm. i'll reverse-engineer it if time permits, but was hoping it was unmolested so we would have an accurate reference, however, it has been so it may not get done for that reason alone. 

i replaced the three 50uFx2 500V cans: one for sure needed it the other two worked but for how long? i had to replace some wiring.

high res shots at the link below.

https://www.dropbox.com/sh/asmsgfzcy1js4ta/AADsHJvEyZzt4KJtO_pfHK2ea?dl=0

--pete

[TIMBO]

NICE.

[uki]

Looks really good !! I'm curious, there is one el84 there, what it does in this amp ?

[jjasilli]

The outside is deceptively clean!     I'm guessing the el84 drives the reverb?, which should sound great.  If so, you can convert, if need be,  to the VibroKing circuit which uses an el84 reverb driver.  IOW you can replace the tank that way.

[Paul1453]

DummyLoad,

Your purchase of this amp almost had me going crazy bidding on this item this morning.

http://www.ebay.com/itm/381549169483

I went to $150 not including shipping and was outbid.

It too had a Quad EL34 output section supposedly putting out 110 Watts.   

I have no idea what I thought I was going to do with a 110 Watt amp.   

I was mostly interested in hearing how a Quad of EL34s sounds.   

I don't have any EL34 tubes in my tube inventory.   

[PRR]

> 300 bux was probably too much

Agree.

These ARE nice amps, but get zero respect in the US; and this one has been seriously molested.

It also smells like a "bitsa" build. TWO OTs?? Yeah, they had a good 50W OT and got an order for 100W amps, they used what they had. The EL84 rev-drive is probably a loose-end; the builder of Elks (and late UniCord) tended to use dissimilar-triode reverb drive, but maybe came up one unit shy.

Some "Elk-type" UniCords use an odd tremolo. The LFO is standard phase-shift. The VCA is a 12AU7, both halves wired back-to-back (plate to cathode) as a bi-directional variable resistor. See Doug's U-1226 schem. I remember it worked in the 1970s. Later simulations say it doesn't work with simulated generic triodes. I think some real triodes do work because the curves go through and past the 0-0 point, and the simulated triodes don't model the corners well. If you get grid-shimmy but no real audio shimmy, try various twin-triodes at this point. (Or you may have a completely different scheme-- I think the Elk-plant dude was creative and did different things in different amps, maybe even in the same-model amps in different batches.)

[DummyLoad]

thanks guys. yes EL84 is for reverb drive. the reverb recovery ckt uses a transformer as well. i suspect it is a balanced return from the tank.

this thing is odd: the LTPI uses 1/2 of the 6AQ8 and 1/2 of a 12AX7. the other half the 6AQ8 is the reverb recovery and the other half of the 12AX7 is the trem oscillator.

the second channel used a 12AU7 and that was very anemic. i replaced the 12AU7 with a 12AX7 - much, much better. 

--pete

[DummyLoad]

tremelo fixed. just needed a footswtch. bought a banjo center dual footswitch rig with TRS 1/4" all good now. now i have reverb on/off and trem on/off.

had a scare. blew a fuse tapping on reverb tank. replaced 3A fast acting w 3A slowblo. blew again. this time i noticed one my newsed 99 vintage electro-harmonix el34 was arcing before popping new fuse. replaced with a quartet of svetlana el34s and new fuse. all is well now.

--pete

[terminalgs]

coincidently, I stumbled on this Elk history just the other day:


http://www.offsetguitars.com/forums/viewtopic.php?f=41&t=94865

[DummyLoad]

thanks TGS.


flipped mine tonight. new owner is very happy.


--pete

[kagliostro]

I missed this your's score Pete

Very Nice equipment

Franco

[JZRepair]

i'll reverse-engineer it if time permits, but was hoping it was unmolested so we would have an accurate reference, however, it has been so it may not get done for that reason alone. 

Did you have a schematic for this?  Or were you able to RE it?  A buddy of mine just dropped his off and closest schematic I can find is for the Bass 100 which has some major differences in the preamp.  Was hoping I wouldn't have to RE it myself.

[DummyLoad]

i'll reverse-engineer it if time permits, but was hoping it was unmolested so we would have an accurate reference, however, it has been so it may not get done for that reason alone. 

Did you have a schematic for this?  Or were you able to RE it?  A buddy of mine just dropped his off and closest schematic I can find is for the Bass 100 which has some major differences in the preamp.  Was hoping I wouldn't have to RE it myself.

Sorry no schematic as I did not RE. IMO, they aren't worth the effort. I got the I bought running and it's been sitting in it's flight case ever since.

-Pete

[JZRepair]

replaced 3A fast acting w 3A slowblo.

The one I'm working on has a 10A fuse in it.  Did you find that the 3A fuse was the way to go?  I see the VKB100 used a 5A fuse, so I am curious about this. 

One other question, what kind of load did you hook up?  Going again off of VKB100, I'm a bit confused.  The jacks are in series on this and the OT's are in series.  If I'm reading this right, and understanding correctly, then I would think it's an 8 Ohm output.  Is this correct?

[astronomicum]

Some "Elk-type" UniCords use an odd tremolo. The LFO is standard phase-shift. The VCA is a 12AU7, both halves wired back-to-back (plate to cathode) as a bi-directional variable resistor. See Doug's U-1226 schem. I remember it worked in the 1970s. Later simulations say it doesn't work with simulated generic triodes. I think some real triodes do work because the curves go through and past the 0-0 point, and the simulated triodes don't model the corners well. If you get grid-shimmy but no real audio shimmy, try various twin-triodes at this point. (Or you may have a completely different scheme-- I think the Elk-plant dude was creative and did different things in different amps, maybe even in the same-model amps in different batches.)

This VCA is used on a number of Univox models including the U320 and U1221 among others. I have found the circuit to work well but it is prone to hum, on these models anyway, which can be minimized through some tube rolling. I have tested nearly a dozen types, including some advertised balanced units, and the best results come from vintage Mullards. I also found that checking and adjusting the bias, which on the models I have worked on are between -1.5V and -3.3V, helps.

[DummyLoad]

replaced 3A fast acting w 3A slowblo.

The one I'm working on has a 10A fuse in it.  Did you find that the 3A fuse was the way to go?  I see the VKB100 used a 5A fuse, so I am curious about this. 

One other question, what kind of load did you hook up?  Going again off of VKB100, I'm a bit confused.  The jacks are in series on this and the OT's are in series.  If I'm reading this right, and understanding correctly, then I would think it's an 8 Ohm output.  Is this correct?

Amp is long gone and most of mt memory of it as well. My apologies. I flipped it to a gentleman that played it, fell in love with it, and just had to have it, so I sold it to him for small profit. I don't know if he still has it as we haven't conversed much since 2017 or thereabout. As stated I used a 3A slo-blo and it seemed fine with that. IIRC, and looking through some photos that I took, construction was not conducive to an easy schematic capture, + the opportunity to flip it quickly prevailed.

Regards,


--Pete

[JZRepair]

Amp is long gone and most of mt memory of it as well. My apologies. I flipped it to a gentleman that played it, fell in love with it, and just had to have it, so I sold it to him for small profit. I don't know if he still has it as we haven't conversed much since 2017 or thereabout. As stated I used a 3A slo-blo and it seemed fine with that. IIRC, and looking through some photos that I took, construction was not conducive to an easy schematic capture, + the opportunity to flip it quickly prevailed.

Yeah, my buddy really wants it fixed up and the ability to use it again, so flipping on my end isn't an option.  Schematics don't line up, with the Twin-50 and the VKB100 (close, but not close enough), so I'm mapping it out myself.  Since I can't find a schematic and I need one, I'll make my own and contribute to the community with what I can. 

Both OTs have labels on them "4 Ohm  0" and the OTs are in series, so I'm going to just reason that it's an 8 Ohm total load.  The two jacks being in series, also suggest it matches with the Twin-50's 4 Ohm speaker and the wiring, as well as it being the same part numbers, match up with the VKB100 with two 4 Ohm loads in series.

He stated when he purchased it, the guy told him it was a 16 Ohm load.  Seemed to work for awhile like that, but eventually, combined with the 10A fuse, he powered it on and the thing started smoking profusely.  I can see some "charring" on one of the OT's, but I can't see anything else that would suggest what burnt up.  Tested the OTs for continutity and there are no shorts, but, we shall see when I get it hooked to power.  Just want to get some of the safety concerns resolved first.  I know a lot of them did it like this in the old days, but I never feel comfortable seeing a Ground being switched, while a Hot wire is left in play, nor do I like when they fuse the Neutral.

Once I get this thing RE'd, I'll post the schematic so the rest of the community has it.  Someone, somewhere, will eventually run into another one of these and hopefully this will help.

[Arjan K]

I bought one of these amps for 35 Euro's earlier this year, complete with two 12 inch Fane speakers in two separate cabinettes.

I've been playing it without the pre amp tubes for tremolo and reverb because they're bad, reverb worked with this tubes in place but the amp would get noisy after 10 minutes, just ordered new tubes.

As you stated OT's are in series so it's a total of 8 Ohm load.
On mine the output jacks are in parallel, I mostly use it with one 8 Ohm speaker (this would not work if output jacks where wired in series) at home .
The previous owner had it for over 20 years and used it with two 8 Ohm speakers in parallel (so that's a 4 Ohm load) without any issues.

10A fuse is a bit to much I think, I'm running mine with a 2A but that's on 230V (I assume yours is on 110V?) and i've never crancked the volume past halfway.

I agree with the ground switch, I've disabled it right away because where I live you have a 50% chance (because you can connect a plug to a socket both ways) of connecting the phase to ground that way!
 
The author of this post says he has a schematic, don't know if he's still active on this forum though.
https://el34world.com/Forum/index.php?topic=15713.msg152554#msg152554

[JZRepair]

I bought one of these amps for 35 Euro's earlier this year, complete with two 12 inch Fane speakers in two separate cabinettes.

I've been playing it without the pre amp tubes for tremolo and reverb because they're bad, reverb worked with this tubes in place but the amp would get noisy after 10 minutes, just ordered new tubes.

As you stated OT's are in series so it's a total of 8 Ohm load.
On mine the output jacks are in parallel, I mostly use it with one 8 Ohm speaker (this would not work if output jacks where wired in series) at home .
The previous owner had it for over 20 years and used it with two 8 Ohm speakers in parallel (so that's a 4 Ohm load) without any issues.

10A fuse is a bit to much I think, I'm running mine with a 2A but that's on 230V (I assume yours is on 110V?) and i've never crancked the volume past halfway.

I agree with the ground switch, I've disabled it right away because where I live you have a 50% chance (because you can connect a plug to a socket both ways) of connecting the phase to ground that way!
 
The author of this post says he has a schematic, don't know if he's still active on this forum though.
https://el34world.com/Forum/index.php?topic=15713.msg152554#msg152554

Thanks for that info.  I actually found a guy in Japan that was able to verify some of this information.  I reverse engineered it and created a schematic.  I am intending on posting that here for anyone who might need/want it in the future.  Once I plotted everything out, the output made complete sense.  My buddy stated he was sold this amp and told that it was a 16 Ohm output.  Yes, 8 Ohm total, but using both jacks, you could hook up two 16 Ohm speakers as the switch in the Output One jack puts the two jacks in parallel.  So, I'm now wondering if he misunderstood when he bought it.  However, it's possible that is what caused the issue of it smoking was an OT and a 16 Ohm load.

According to the guy in Japan, the OTs are incredibly rare and he knows quite a few shops there that have a number of these amps sitting around, because they're trying to find suitable replacements.  There's a transformer rebuilder near me that I might see if they can rewind them both, if that seems to be the problem.

As far as the fuse goes, the PT has a MAX output (from what I can gather) of just under 6A.  And yes, I'm on 110V, but I figure 6A is the max the PT could handle, I'm thinking I'll start with a 3A SB and go from there.  If I blow the fuse, then I can bump it up a little bit and go from there, but from what I understand, 3A would have been pretty common for amps this size that came out of Japan.

First things first though, tomorrow morning, I'm going to plug it into the current limiter and make sure I have no dead shorts under power.  Hoping for the best, but it hasn't been used in 20 years, I'm figuring the caps are all garbage by now and I'm expecting more issues to resolve right off the bat.  I'll probably end up pulling all the tubes just to be safe for a first go.

[PRR]

> the OTs are incredibly rare and he knows quite a few shops there that have a number of these amps sitting around, because they're trying to find suitable replacements.

50W 2-EL34 to 4 Ohm are as common as tea-shops; while not "authentic" it would play better than two blown transformers. And yes they can be rewound; unless some previous tech took them off and lost them.

Total efficiency of a EL34 amplifier including plates screens and heaters (and reasonable preamp) is better than 40%. So a 100W amp is 250W off the wall, or 3A @ 120V or 1.5A (1600mA) @ 240V. You might round-up by 1.5X but 6A seems mighty generous.

[JZRepair]

> the OTs are incredibly rare and he knows quite a few shops there that have a number of these amps sitting around, because they're trying to find suitable replacements.

50W 2-EL34 to 4 Ohm are as common as tea-shops; while not "authentic" it would play better than two blown transformers. And yes they can be rewound; unless some previous tech took them off and lost them.

Total efficiency of a EL34 amplifier including plates screens and heaters (and reasonable preamp) is better than 40%. So a 100W amp is 250W off the wall, or 3A @ 120V or 1.5A (1600mA) @ 240V. You might round-up by 1.5X but 6A seems mighty generous.

Thanks for that bit of info!  I was initially thinking of a 5A fuse, because of the VKB-100.  Under this logic though, 3.5A-4A might be a better choice to give it a little headroom, while forcing it to blow before any major damage.  That's what got me with the 10A.  He said it was smoking pretty bad, but the fuse never blew.  I know from other electronics, the fuse should blow to protect the rest of the system if one component has a major failure.  So I didn't want to go too low, or even too high, because I want that "sweet spot" where everything functions as it should, but cuts the power when a major malfunction occurs.

[DummyLoad]

Fender Twin uses a 4A SB with 120V mains - I used a 3A SB without issue. Better to error on the side closer to failure in this case.

https://reverb.com/item/19296693-1975-fender-twin-reverb-silverface-tube-guitar-amplifier-orange-jbl-d120f-34502

--Pete

[Arjan K]

I am intending on posting that here for anyone who might need/want it in the future.

I would be very interested in that schematic!

[JZRepair]

I am intending on posting that here for anyone who might need/want it in the future.

I would be very interested in that schematic!

I'll make sure I post it once the repair is completed.  I want to double-check some things, change the layout slightly (for the reverb/tremelo portion), and make sure I have all the values correct.

[JZRepair]

As promised, I've included a link to the PDF of the schematic.  Now, I can't completely guarantee there aren't any errors, so if you find any with any other existing VK100's out there, I'd love the feedback so I can update your findings.  I completed the repair, replacing all the electrolytics, putting in new power tubes, biasing, and that pretty much covered it.  I did do some rewiring which is only reflected in the schematic.  So care should be taken if you have an unaltered VK100.

Mainly, the rewiring consisted of removing the death cap/ground switch (left in for aesthetics, but removed from the circuit), rewiring the mains so the line was fused and that required moving the neutral off of the 117/110 switch.  I chose to leave the two-prong power plug in play, just because I didn't feel like messing with it.  If you use these schematics, you use them at your own risk, understanding there might be a few errors here and there and I had to make some judgement calls based on observations with regards to components.

I did not really do much for logging the voltages.  I can tell you that biasing got me -43.1V across the bias resistor, 476V on the plates, with about 32mA of current through the plates.  I didn't add the voltages other than the negative bias voltage, because I didn't really see a need.

So, here you go.  Let me know what you think.
https://www.jaerllc.com/extras/elk_vk100.pdf

[Arjan K]

Wow, that 's amazing!
I'm going to compare it with mine and let you know what differences I found.
I like the way you split the scheme in different sections, now I can learn how the separate parts work.
Thank you very much! 

[JZRepair]

Wow, that 's amazing!
I'm going to compare it with mine and let you know what differences I found.
I like the way you split the scheme in different sections, now I can learn how the separate parts work.
Thank you very much! 

Thanks, I needed to be able to see it in a way that I understood it.  Breaking into the sections made it a bit easier.  It makes it a bit more difficult to read, but I was less worried about that compared with actually understanding each section.  I really didn't even want to reverse engineer this thing, but the fact that I just couldn't wrap my head around all the connections made it incredibly difficult without it.  I needed to be able to see the flow of the signal so when I had to get that far, I could visualize it on a schematic.

Like I said, I didn't document the voltages.  I also kind of guessed on the resistor sizes.  Being that they are older, I expected them to look bigger, but the ones I labelled as 1/2W might actually be 1W, the 1/4W might be 1/2W, but I calculated out the resistance on the bias (R2) and figured it was only doing less than 1/2W, so I chose half watt for the larger resistors.  The power resistors, I guessed on their wattage as I couldn't find any documentation on them, but I also didn't dig too much, either.

I'm actually thinking if I get the chance, I might even design a PCB for this if anyone wants to build one and put it on a PCB.  I haven't decided yet on that.  The main issue is going to be finding OTs as the guy I spoke with in Japan has stated there's no information about them and he knows shops over there who have stacks of these amps that are waiting for a suitable replacement.  So if anyone is smart enough to figure that out or has one and can find someone who will rewind it, I'd love to be able to put a part number with those.

[Arjan K]

Thanks, I needed to be able to see it in a way that I understood it.  Breaking into the sections made it a bit easier.  It makes it a bit more difficult to read, but I was less worried about that compared with actually understanding each section. 

I had a better look at it today and it's indeed a bit difficult to read this way, I see you made the schematic in  KiCad are you willing to share the KiCad files also? Then I can make a single schematic from it to make it better readable.

[JZRepair]

Let me see what I can do.  I've been pretty busy lately with repairs, but I'll put it on my to-do list and get you another copy with a single page schematic.  Otherwise, if you have KiCad, I am pretty sure most of the components are pretty standard for the symbols.  I think the only ones I made were the PT and reverb tank, but you can always draw it up for yourself based off of mine.

[Arjan K]

Yes I have KiCad installed a few days ago and I've already begun drawing the schematic, so don't bother drawing it, you've done enough!

[DummyLoad]

I found this thread's Viking 100 amp buried in a pile when cleaning and sorting out my storage room for crap to sell - Stuff I'm never going to play. Forgot I had it here. The gentleman that bought it brought it back and swapped for another - I don't recall he ended up with.

This weekend I'll clear off one of the benches and have a look. IIRC, in the copy that I have the EL84 drives the reverb transformer. Rats nest point2point sucks to attempt to reverse engineer. 

--Pete

[JZRepair]

Yes I have KiCad installed a few days ago and I've already begun drawing the schematic, so don't bother drawing it, you've done enough!

Thanks.  Sorry for the bother of it.  I didn't even really want to RE this thing, but my buddy has helped bring a lot of business my way and I wanted to repay him.  This amp was the first amp he ever bought and I wanted to get him going as a token of appreciation for how much he's helped me.  While I was doing it, I figured I should share this with the rest of the community, just because we need this information to stay alive.

Hopefully you won't have too much difficulty getting it switched over to one sheet.  Again, let me know if you find any variances in my schematic.  I keep questioning that return path for the reverb.  For some reason right now, it's not making much sense to me, but I don't have the amp any longer, so I can't verify it.

[JZRepair]

I found this thread's Viking 100 amp buried in a pile when cleaning and sorting out my storage room for crap to sell - Stuff I'm never going to play. Forgot I had it here. The gentleman that bought it brought it back and swapped for another - I don't recall he ended up with.

This weekend I'll clear off one of the benches and have a look. IIRC, in the copy that I have the EL84 drives the reverb transformer. Rats nest point2point sucks to attempt to reverse engineer. 

--Pete

It was a bit of a pain to RE, but overall, the wires were pretty nicely tied up.  My issues were more with the fact that some components were soldered onto the underside of the terminal boards and it was difficult to get enough play on the wires and components to get those boards out to see what the components were.  They were mostly just caps, I believe and electrolytics that I ended up replacing, so it wasn't too much of a problem, but still a huge hassle.  Overall, it was a fun little project, I'm just hoping I got it close to being what it is.  Most of it should be exactly what I saw, but I wouldn't doubt I missed something or made an error somewhere.  It was just nice to use it while getting it back up and running, having something to refer to, rather than try to remember what every component went to.