As promised, I am becoming the JimiLee of small cheapish amps. ;D
I have more new amps than time to post about them, but I'll do this one tonight. First entry was the MonoPrice 5W 6V6 10" combo for $99.
Tonight is the SET5 5W EL84 super-tiny head. It is $99 including shipping. Got it from here. (https://www.ebay.com/itm/California-Electric-Guitar-Amp-All-Tube-Head-SET5-Head/282889242894?epid=20016734329&hash=item41dd83490e:g:OnkAAOSwgd1arep9)
It is a LOT smaller than I thought it would be. See first pic below for size reference (never miss a chance for product placement!). Seems quite well made overall. OT is a little small, but I can't say I expected big iron in a 5W $99 amp.
Here's the specs:
• 5 watts via 1x EL84 and 1x 12AX7 (Chinese tubes, of course)
• Treble, Bass, and Volume controls
• 1W and 0.1W attenuation modes (slide switch on rear)
• 8 and 16 ohm outputs
Frankly, it sounds pretty good. It doesn't have a ton of umph, but it does have a decent tone at full volume. Kinda sounds like a Valve Jr, but with a touch more gain and a little smoother. There's clean headroom with humbuckers up to about 3 or about 4 with single coils. Bass and Treble are actually useful. The 1W setting sounds pretty good with the amp cooking; the 0.1W has too much high cut and frankly isn't loud enough to do anything useful other than rock out next to a sleeping baby. Haven't tested any other tubes in there yet, but I have some in the mail. I don't expect massive improvement with different tubes, but swapping is half the fun of tube amps. :)
Internal build quality was nicer than I expected. And nothing is surface mount. Modding should be relatively easy. I have emailed the distributor and asked for a schematic, so we'll see what happens.
I noticed there are 8 or 10 1/4-watt resistors (and they are carbon film). I assume these guys did the math and feel okay with that low of wattage in certain spots. Also, the "anchor" tabs on the power tube socket were not soldered, so the socket moves more than I like when removing a tube. I will fix that shortly. Some of this appears to be wave soldered, while other components are definitely done by hand. They didn't do any flux cleanup, which isn't the end of the world, but obviously a little on the sloppy side. A few components are little crooked, but I'm being picky.
The cage is actually three pieces, and the front/back grill are removable. I'm totally going to 3D print a new badge for the front.
Overall, it's a nice little amp. Great platform for modding or doing a gut-n-rebuild. But it's also okay just as it is as a tiny amp head for practice or recording. Not a damn thing wrong with it out of the box.
PICS!
(https://i.imgur.com/ys2qBhN.jpg)
(https://i.imgur.com/biiOY8g.jpg)
(https://i.imgur.com/7hXBehl.jpg)
(https://i.imgur.com/v37ztb2.jpg)
(https://i.imgur.com/fUEAzvb.jpg)
That's cool. Hundred bucks for that seems like really good value. Transformers look way better than I expected, and as you say, you could mod it like a madman.
Would be interested to see the schematic, particularly for how they dealt with the power attentuation. From the pick it looks like they're just spilling heat with those metal oxide resistors. Have you poked around the innards at all? Is there more under the board? Am curious.
Quote from: ahiddentableau on May 03, 2018, 03:32:18 AM
Would be interested to see the schematic, particularly for how they dealt with the power attentuation. From the pick it looks like they're just spilling heat with those metal oxide resistors.
Yeah, I think that's the extent of the attenuation. Maybe an added treble bleed cap would improve things? Not sure, but I can definitely give it a try and see what happens.
Quote from: ahiddentableauHave you poked around the innards at all? Is there more under the board? Am curious.
Not yet. Just barely had time to give it a 20-minute test and do a writeup. I'll keep all progress pics and info in this thread.
I think it might be possible to add an additional preamp tube for more gain. But failing that, I think there could be easy mods for negative feedback and probably a pentode/triode switch. And of course, there will be some easy mods for increaseing or decreasing gain via resistors and tightening bass via cap swaps.
im sorry, but im curious
how the sound in 0.1W mode
hey man, dont laugh :D i never play tube in low watt like that
Makes me want to buy one for my bench amp...
Quote from: 287m on May 03, 2018, 05:02:17 AM
how the sound in 0.1W mode
It's very quiet. Like, almost unusably quiet. Guitar string noise can be heard over the amp at the 0.1W setting.
Quote from: culturejam on May 03, 2018, 03:46:09 AM
I think it might be possible to add an additional preamp tube for more gain. But failing that, I think there could be easy mods for negative feedback and probably a pentode/triode switch. And of course, there will be some easy mods for increaseing or decreasing gain via resistors and tightening bass via cap swaps.
Looking forward to this.
One of the things that caught my eye was that the power transformer label says it can put out 2.5A on the filament winding. That's surprisingly generous. If memory serves, an EL84 requires 0.75A, and 12AX7s are 0.3A a piece, I think, so it should be able to power several more tubes. That's cool. If you don't like the amp, it's gonna be really modable.
The distributor provided the schematic!
Interesting setup. The second triode and EL84 look exactly the same as a Valve Jr. (down to the values). Front half is its own thing, as far as I can tell. Not sure about that tone stack setup. It almost looks like a Bassman / Marshall TMB at first, but then I see how Treble is setup differently.
I think it should be easy to implement half a dozen minor mods to this thing without a lot of trouble. Biggest issue is that there just isn't much room to add a lot of hardware. Squeezing another tube in there is going to be tricky, so I might just leave that one alone. But man, adding an EF86 up front would be sweeeeet.
I'll try a few things and put together a quick guide on what I did.
Side note: I put a set of JJs in there tonight. Doesn't per se sound *better*, but it definitely has more breakup now and longer sustain.
I've had the idea to use something like an ECF82 which has both a pentode and triode in it to do like a variation of a Matchless Clubman preamp. Could be a cool application for a little amp like that.
I'm pretty sure on the AX84 forums I saw where someone posted something similar to what I described actually. Triode -> pentode -> power pentode.
Quote from: Aristatertotle on May 04, 2018, 06:34:45 AM
I've had the idea to use something like an ECF82 which has both a pentode and triode in it to do like a variation of a Matchless Clubman preamp. Could be a cool application for a little amp like that.
I'm pretty sure on the AX84 forums I saw where someone posted something similar to what I described actually. Triode -> pentode -> power pentode.
Wow, talk about timing. I just bumped into something like this the other day on Merlin Blencowe's page. He offers a set of PCB boards for amp prototyping, and just released a board for the ECL86--almost precisely what you're talking about, a triode/SC pentode combo tube. If you're interested in checking it out, here's the link:
http://www.valvewizard.co.uk/ecl86pcb.html (http://www.valvewizard.co.uk/ecl86pcb.html)
Quote from: ahiddentableau on May 04, 2018, 11:13:57 AM
Quote from: Aristatertotle on May 04, 2018, 06:34:45 AM
I've had the idea to use something like an ECF82 which has both a pentode and triode in it to do like a variation of a Matchless Clubman preamp. Could be a cool application for a little amp like that.
I'm pretty sure on the AX84 forums I saw where someone posted something similar to what I described actually. Triode -> pentode -> power pentode.
Wow, talk about timing. I just bumped into something like this the other day on Merlin Blencowe's page. He offers a set of PCB boards for amp prototyping, and just released a board for the ECL86--almost precisely what you're talking about, a triode/SC pentode combo tube. If you're interested in checking it out, here's the link:
http://www.valvewizard.co.uk/ecl86pcb.html (http://www.valvewizard.co.uk/ecl86pcb.html)
Merlin has some cool stuff, I've got two his books.
The ECL86 is a combo triode with a power tube in one. I meant more like the combo of a triode and a small signal pentode. I know there are some that are essentially a 12ax7 and an EF86 in one tube.
Those ECL86's are super cool though. One of those with a 12ax7 in front could give you a nice range of dirt options. Just that extra bit of oompf over a valve Jr.
Quote from: culturejam on May 04, 2018, 04:31:45 AM
The distributor provided the schematic!
Interesting setup. The second triode and EL84 look exactly the same as a Valve Jr. (down to the values). Front half is its own thing, as far as I can tell. Not sure about that tone stack setup. It almost looks like a Bassman / Marshall TMB at first, but then I see how Treble is setup differently.
I think it should be easy to implement half a dozen minor mods to this thing without a lot of trouble. Biggest issue is that there just isn't much room to add a lot of hardware. Squeezing another tube in there is going to be tricky, so I might just leave that one alone. But man, adding an EF86 up front would be sweeeeet.
I'll try a few things and put together a quick guide on what I did.
Side note: I put a set of JJs in there tonight. Doesn't per se sound *better*, but it definitely has more breakup now and longer sustain.
It's pretty cool of them to send the schematic. Seems like a lot of companies are refuseniks on that account. Anyway, thanks for posting it.
As you said, it's a pretty standard design (I mean that in a good way - very modable). As far as I can see, the tone stack is basically your standard passive Baxandall with a bright cap and a couple cap changes off the treble control. They removed the cap on the wiper and added an extra cap to ground. How do you find it? IMO, at low volume amps generally need a really heavy-handed approach to tone control in order to compensate for the whole Fletcher-Munson effect thing. But it doesn't look like they've done too much here.
the hammond ao-44 amplifier carried a pair of ecl86 and by grafting a preamp tube instead of a transistor you get a nice little guitar amp with a tiny footprint ... fun tubes to play with. in a single ended amp you'd be pretty short on watts unless that was your design goal
Quote from: Aristatertotle on May 04, 2018, 11:36:31 AM
Those ECL86's are super cool though. One of those with a 12ax7 in front could give you a nice range of dirt options. Just that extra bit of oompf over a valve Jr.
I've dreamed of this for years! ECL86 + one 12ax7 and you could have a single-ended JCM800! Definitely going to check out the Merlin info / boards on this.
Also, I bought a 6AF11, which is two triodes and a power pentode in one bottle. I've seen a few projects that are billed as "Champ in a bottle". I've also read it can be really noisy from the close proximity of the triodes, but these guys seem to make it work out: https://zeppelindesignlabs.com/product/percolator-2w-amp-kit/ Probably the metal shields they put between the transformers and the tube that do the trick.
Quote from: ahiddentableau on May 04, 2018, 11:47:02 AM
How do you find it? IMO, at low volume amps generally need a really heavy-handed approach to tone control in order to compensate for the whole Fletcher-Munson effect thing. But it doesn't look like they've done too much here.
It's quite effective, in my opinion. At full volume, there's more treble and bass than most people would need, so dialing back is nice. But at low volume, you gotta crank those back up to keep it sounding decent.
Tone stack bypass switch might be a neat thing to add. Seriously, I'm thinking about buying a second one. It sounds pretty damn good as is, and it would be nice to have a stock unit to do a real comparison and not just have to rely on listening memory (which is anything but reliable). Or I could do a high-gain mod on one and clean headroom mod on the other. So cheap!
Thanks for posting these reviews, I'm in the market for a cheap low wattage small gig/open mic amp
Okay, I'm going to need to walk back a comment I made about the 0.1W setting. When I first listened to it, I had just done 20 minutes of playing/listening in the 5W setting. So of course it sounded quite and like all the highs had been chopped off.
Listening again tonight with fresh ears, it's actually decent sounding. Loud enough for having a little solo fun, definitely. And without having just had your ears pummeled with full 5W volume, the highs are decent enough.
Also, I swapped out the JJ EL84 I had in there with a reissue Tung-Sol. I actually like it better.
Looks interesting, have fun modding it! Looking forward to hear what you come up with and find useful.
Here's a good general easy terms write up of modding amps with some suggestions, could be useful.
Attached pdf.
Quote from: cooder on May 12, 2018, 10:51:03 PM
Looks interesting, have fun modding it! Looking forward to hear what you come up with and find useful.
Here's a good general easy terms write up of modding amps with some suggestions, could be useful.
Attached pdf.
Awesome, thanks!
Another great site of wisdom is
https://robrobinette.com/Amp_Stuff.htm (https://robrobinette.com/Amp_Stuff.htm)
with a bunch of mod tips like Marshall stuff:
https://robrobinette.com/How_the_Marshall_JCM800_Works.htm (https://robrobinette.com/How_the_Marshall_JCM800_Works.htm)
and of course Merlin / Valvewizard:
http://www.valvewizard.co.uk/ (http://www.valvewizard.co.uk/)
That is definitely tone-per-buck worthy! You can't build the same amp for this price.
I also build a small amp in a lunchbox using an ECL86, and it was loud enough. There was not that much distortion on tap though.
I built something with the PCF802 and a PCL82. Heaters in series and high voltage from a quintupler voltage multiplier using only caps and diodes. Really cool for what it is. The triode in front of the pentode overdrives it pretty nicely. The PCL82 is much cheaper than the ECL82 or the ECL86.
The matchless circuit would be interesting to give a try.
Quote from: culturejam on May 03, 2018, 01:28:55 AM
As promised, I am becoming the JimiLee of small cheapish amps. ;D
I felt another disturbance in the force. It's nice to be able to do things like this isn't? Those look great man.
I didn't tell you guys I bought a fender ash body tele, got a great deal on it. I also traded for another G&L tele and a red fender mustang. Good times!
Sent from my iPhone using Tapatalk
I've done some more listening of this amp. I'm really liking it better and better. All cranked up, it's got gain in the range of what I would call "Classic AC/DC". There's some great breakup, but it's pretty dynamic and uncompressed. Sounds great with humbuckers, but I haven't tested it with singles yet (only coil-cut on my PRS).
There's not a lot I want to change about the tone, but I think I'm going to try two simple mods that will allow for both more and less clean headroom:
1) First is to toggle the series input resistor value. Stock is 68K, so my plan is to use a DPDT center-off and have two parallel value options (say, like 33K and 10K as the final value). This gives stock, and two levels higher gain.
2) Then I want to change the bypass cap value on V1a. Also using a DPDT center-off, I will pull the stock 22uf from the board and move it to one throw of the switch, and have something like 680n or 1uf on the other side. So that would give two boosted options and no bypass cap for minimum gain.
Optional: I'm considering doing negative feedback as well, but I'll do that if I don't think the other two mods makes enough difference on the clean headroom front.
Quote from: culturejam on May 18, 2018, 02:31:04 AM
1) First is to toggle the series input resistor value. Stock is 68K, so my plan is to use a DPDT center-off and have two parallel value options (say, like 33K and 10K as the final value). This gives stock, and two levels higher gain.
2) Then I want to change the bypass cap value on V1a. Also using a DPDT center-off, I will pull the stock 22uf from the board and move it to one throw of the switch, and have something like 680n or 1uf on the other side. So that would give two boosted options and no bypass cap for minimum gain.
Optional: I'm considering doing negative feedback as well, but I'll do that if I don't think the other two mods makes enough difference on the clean headroom front.
Just my two cents for this:
1) I don't think you will hear much if any difference changing the 68K resistor as it's just a grid stopper resistor for V1 to avoid blocking distortion happening. It won't have much effect on gain or input, me thinks. Before you commit to drilling a hole for that switch I would test it and see if it makes any difference at all. My bet is none that you could hear.
2) will have a much more profound effect and there's a cool Uncle Doug video and a neat calculator how it not only affects gain but most of all also bass response.
https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/ (https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/)
http://bmamps.com/CapCal.html (http://bmamps.com/CapCal.html)
Negative feedback can have a very worthwhile and noticable difference, depends on amp. Worth a try I'd say.
Thanks, Cooder.
I thought about doing the grid stopper mod because it actually made a difference in the Valve Jr circuit back when I modded mine. Or at least I think it did. ;) Maybe I'll table that one and focus on the other two.
That video is great! Thanks for sharing.
Do you have any preferences on implementing negative feedback on a circuit like this one? I've seen it set up a few different ways.
You could also consider changing plate resistor R 3 (in schem 220K).
For lower gain take a lower value, like 100K (very common) or maybe 150K.
You could trying upping that value for more and see what happens, sometimes it gives squealing and self oscilation as downside. In any case that will be a noticable difference...
I'll have a quick look what i can find re negative feedback.
Negative feedback: if you google 5F1 schematic it may be easiest to see what happens there and how to apply it in your amp.
It would be as far as I can tell in your amp a connection with some resistance (in Fender 5F1 its 22 K at 4ohm OT tap).
The amount of negative feedback depends also on which OT tap (you have 8 and 16ohm) you take it from and what resistance would work best.
As that's overall anyway a matter of taste you might want to add a variable negative feedback with a 50K pot and a 22k resistor in series. You always want some resistance in circuit otherwise the signal will be completely cancelled off.
You could do a 1M pot which basically gives you zero neg feedback to 22K neg feedback, downside would be a coarse dial in as the 1M pot is very fast changing.
Or make it switchable. Switch to disengage (which is stock) and switch position with a 22K and a 56 K resistor (spdt on/off/on).
There's calculators to figure out amount of neg feedback based on resistor value and which tap you take it from.
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#3-Way_Negative_Feedback_Switch (https://robrobinette.com/Generic_Tube_Amp_Mods.htm#3-Way_Negative_Feedback_Switch)
And this mod on V1 could be interesting too to tame and tune drive sound. I've seen it for example in Dumble and Soldano amps.
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Preamp_Local_Negative_Feedback (https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Preamp_Local_Negative_Feedback)
Here's a neat way to implement the Bias cap switching on V1:
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#3-Way_Preamp_Bias (https://robrobinette.com/Generic_Tube_Amp_Mods.htm#3-Way_Preamp_Bias)