2Watt Sub Miniature Plexi

[Structo]

Nice job on the cabinets!

Probably too late but a trick I have used when repairing binding on guitars is to take a scrap and put it in a small jar.
Then add a little bit of acetone.
It will dissolve the plastic making a paste in consistency. (don't add too much acetone)
This will bond with the existing binding.

But it depends what the material is made from for it to work.

[skyclmbr]

Thanks!

That's another good tip for the plastic that I'll have to try. I may actually try that to fill in some of the gaps that occured with my less than stellar trimming job.

Also, Dana, am I correct in that the OT can't be wired for a 16 ohm output? I'm interested in maybe making it have a 16 ohm speaker jack in addition to the 8 ohm to run in through the typical Marshall cabinets. Those are usually 16 ohms, right?

Thanks!
Bryan

[skyclmbr]

Thanks!

That's another good tip for the plastic that I'll have to try. I may actually try that to fill in some of the gaps that occured with my less than stellar trimming job.

Also, Dana, am I correct in that the OT can't be wired for a 16 ohm output? I'm interested in maybe making it have a 16 ohm speaker jack in addition to the 8 ohm to run in through the typical Marshall cabinets. Those are usually 16 ohms, right?

Thanks!
Bryan

Oh wait. Marshall 4x12 cabs are 8 ohm stereo and 4/16 ohm mono? Obviously I haven't played outside the house ever since I don't know this...

[JazzGuitarGimp]

Hi Dana,

I've been meaning to ask this question also. What is the preferred output impedance of the MicroPlex? I've got just a few hours worth of work to finish mine. Looking forward to it!

Cheers,
Lou

Thanks!

That's another good tip for the plastic that I'll have to try. I may actually try that to fill in some of the gaps that occured with my less than stellar trimming job.

Also, Dana, am I correct in that the OT can't be wired for a 16 ohm output? I'm interested in maybe making it have a 16 ohm speaker jack in addition to the 8 ohm to run in through the typical Marshall cabinets. Those are usually 16 ohms, right?

Thanks!
Bryan

[skyclmbr]

I think it's 8 ohms, that's what I've been using. But I'll defer to Dana for the final answer.

[UR12]

I think it's 8 ohms, that's what I've been using. But I'll defer to Dana for the final answer.

The Microplex is setup for 8 ohms. I have looked at adding a tap but its rough trying to get it down to the size it is and still keep the tone. I can have one built for 16 or 4 ohm but too many taps would alter the physical size of the tranny and require a lot of work to get it to fit on the board and keep the amp as small as it is. If you look at the Hammond off the shelf stuff you will see that it has a frequency range starting at 150hz before it starts rolling off. Our tranny is wound to go down to 80hz to cover the full range of a guitar in standard tuning. Small wattage amps IMHO all suffer from weak bass response and this is mostly caused by Fletcher-Munson and the way we percieve sound. The OT on the Lil Devil and the Microplex are both wound with more inductance which translates to more windings to be able to get the desired freq response. More windings means larger physical size. believe it or not the wire used is so small that the trannys have to be hand wound as the wire is too small to fit in the winding machines. I look forward to hearing from you guys on what you think of the bottom end on the Microplex. I also appreciate your comments on what you think would make the amp better, so by all means keep the suggestions coming and if I can find a way to incorporate them I will do my best to accommodate. Sometimes you have
to make compromises and 8 ohms instead of 4/8/16 is one I had to make.

[skyclmbr]

The Microplex is setup for 8 ohms. I have looked at adding a tap but its rough trying to get it down to the size it is and still keep the tone. I can have one built for 16 or 4 ohm but too many taps would alter the physical size of the tranny and require a lot of work to get it to fit on the board and keep the amp as small as it is. If you look at the Hammond off the shelf stuff you will see that it has a frequency range starting at 150hz before it starts rolling off. Our tranny is wound to go down to 80hz to cover the full range of a guitar in standard tuning. Small wattage amps IMHO all suffer from weak bass response and this is mostly caused by Fletcher-Munson and the way we percieve sound. The OT on the Lil Devil and the Microplex are both wound with more inductance which translates to more windings to be able to get the desired freq response. More windings means larger physical size. believe it or not the wire used is so small that the trannys have to be hand wound as the wire is too small to fit in the winding machines. I look forward to hearing from you guys on what you think of the bottom end on the Microplex. I also appreciate your comments on what you think would make the amp better, so by all means keep the suggestions coming and if I can find a way to incorporate them I will do my best to accommodate. Sometimes you have
to make compromises and 8 ohms instead of 4/8/16 is one I had to make.

Thanks for the answer Dana! I would agree that you made the right decision to compromise the # of taps vs the frequency response. I have to say that with the 1x12 G12H30 clone it's got quite a good low end. I wouldn't say it has as much as the Fender Hot Rod Deluxe that I sold off, but that's known as a particularly bass-heavy amp, and the G12H30 speaker is not a particularly bass-heavy speaker. With the 4x8 Jensen Mod 8's, there's a bit less bass and certainly a very different tone. We'll see how it records tonight, but they are both very pleasing in their own ways. The 4x8 sounds more "Marshally", and sounds like it would (to use the well-worn phrase) "cut through the mix" better. The 1x12 sounds more bass-heavy, less high end detail, but with a very satisfying flavor that's hard to describe in words. Hints of oaky nuttiness with overtones of blueberry, perhaps? I dunno. The 1x12 is also open back and the 4x8 is closed back, which I can change to try and get a more blueberries-to-blueberries comparison.

Apologies for this ramble, I think at the end of the day I appreciate the slightly lower levels of bass in the 4x8 and the focus that a closed cab gives you because, when coupled with the VVR circuit in the Microplex, it means you can play very quietly, hear a lot of detail, and not wake up or anger the significant other. Will record some tonight and post!

I'm also slated to go try it out in my guitar teacher's 4x12 cab as well, so I'll report on that too (although it sounds like you've already played it through a 4x12 cab, Dana).

Thanks,
Bryan

[UR12]

Hey that looks sweet! I've been running mine through my 4x12 loaded with 70s greenbacks. it's an old vox 4x12 design with a port across the back so it's not sealed but still has a good chunky bottom end. I am also running it through a EV TL806 1x12 ported cab loaded with a Fane Medusa 150 (103db 1w/1m) I get 3db additional SPL and that combination is pretty loud for a two watt amp. We have a local guitar/amp show coming up here on the 16th and I will have both the Lil Devil and the Microplex for people to try out side by side. I did get to compare the Microplex amp to a vintage 76 1987 Marshall, side by side and they sounded pretty close both in tone and response. Once I get the Microplex nailed down I think I will start working on a miniature Vox with a subminiature 6205 pentode front end. Should be fun. Just wish I had more time to experiment

[MCK]

Once I get the Microplex nailed down I think I will start working on a miniature Vox with a subminiature 6205 pentode front end. Should be fun. Just wish I had more time to experiment

Dana I think you're on a roll here!!! How about a sub-miniature Dumble build at some point? I can also see a nice SLO take at some point. How about it?

[skyclmbr]

Hey that looks sweet! I've been running mine through my 4x12 loaded with 70s greenbacks. it's an old vox 4x12 design with a port across the back so it's not sealed but still has a good chunky bottom end. I am also running it through a EV TL806 1x12 ported cab loaded with a Fane Medusa 150 (103db 1w/1m) I get 3db additional SPL and that combination is pretty loud for a two watt amp. We have a local guitar/amp show coming up here on the 16th and I will have both the Lil Devil and the Microplex for people to try out side by side. I did get to compare the Microplex amp to a vintage 76 1987 Marshall, side by side and they sounded pretty close both in tone and response. Once I get the Microplex nailed down I think I will start working on a miniature Vox with a subminiature 6205 pentode front end. Should be fun. Just wish I had more time to experiment

Thanks!

I didn't get a chance to record with the different cabs, but here's a couple sound clips I recorded back over Thanksgiving. They're not much but they're at least some examples of the amp sounds through the 1x12 G12H30 and with some different guitars. Three files, using a PRS Mira, a "strat", and an old Harmony archtop with a jazz thin humbucker in the neck position. My girlfriend's bro is just playing chords and lines while I mess around with all the knobs on the amp. At one point a Boss Fender Reverb is on but other than that no pedals.

[JazzGuitarGimp]

Hi All,

I've got mine up and running, though I have excessive 60Hz hum. I've tried wiring the grounds in various ways to no avail. Hum goes away the instant I turn the power off, so I am thinking it's a wiring issue. Has anyone successfully finished their build without hum? If so, care to share how you did the chassis, PT, and inter-board wiring? Specifically:

- Where di you connect the heater winding CT?
- Where di you connect the High Voltage winding CT?

Many thanks,
Lou

[skyclmbr]

Hi All,

I've got mine up and running, though I have excessive 60Hz hum. I've tried wiring the grounds in various ways to no avail. Hum goes away the instant I turn the power off, so I am thinking it's a wiring issue. Has anyone successfully finished their build without hum? If so, care to share how you did the chassis, PT, and inter-board wiring?

Many thanks,
Lou

I'll try and take a couple pictures of my wiring and show you. I had trouble with the power switch but that resulted in the power being applied when the switch was off, not really any hum.

[JazzGuitarGimp]

Hi All,

I've got mine up and running, though I have excessive 60Hz hum. I've tried wiring the grounds in various ways to no avail. Hum goes away the instant I turn the power off, so I am thinking it's a wiring issue. Has anyone successfully finished their build without hum? If so, care to share how you did the chassis, PT, and inter-board wiring?

Many thanks,
Lou

I'll try and take a couple pictures of my wiring and show you. I had trouble with the power switch but that resulted in the power being applied when the switch was off, not really any hum.

Hi Skyclmbr,

Please hold off on the pics:

My hum goes away when I pull V2. I've got more troubleshooting to do. But at this point, I'm thinking my chassis / PT / board wiring is okay. I'll report back when I get it sorted out / or / need help.

Many thanks,
Lou

[skyclmbr]

Hi All,

I've got mine up and running, though I have excessive 60Hz hum. I've tried wiring the grounds in various ways to no avail. Hum goes away the instant I turn the power off, so I am thinking it's a wiring issue. Has anyone successfully finished their build without hum? If so, care to share how you did the chassis, PT, and inter-board wiring?

Many thanks,
Lou

I'll try and take a couple pictures of my wiring and show you. I had trouble with the power switch but that resulted in the power being applied when the switch was off, not really any hum.

Hi Skyclmbr,

Please hold off on the pics:

My hum goes away when I pull V2. I've got more troubleshooting to do. But at this point, I'm thinking my chassis / PT / board wiring is okay. I'll report back when I get it sorted out / or / need help.

Many thanks,
Lou

Ok, no prob. Good luck!

[JazzGuitarGimp]

Hi All,

I am having an issue with hum and I'd like to ask the collective for any suggestions. Here is what I know at this point:

The hum (60Hz) goes away if I remove V2, or if I ground the grid of V2A.
There doesn't appear to be any oscillation at V2A anode. Hum also goes away as soon as I turn off the power switch.

Also, I did a quick scan of all the pages of this thread, and it doesn't look like anyone has posted a voltages chart yet. Here are my voltages with all tubes installed, and all controls except VVR all the way down. VVR is all the way up.

B+: 177.3
Output plates: 172.2
Output Screens: 167.6
PI: 136.1
V2: 115.8
V1: 106.3
Bias: -32.9

V1A a: 71.8
V1A k: 0.957
V1B a: 50.0
V1B k: 0.466

V2A a: 116.0
V2A k: 68.3
V2B a: 67.7
V2B k: 0.296

V3A a: 85.0
V3A k: 16.89
V3B a: 82.5
V3B k: 16.89

V4 a: 170.3
V4 g2: 166.8
V4 g1: -32.14

V5 a: 170.9
V5 g2: 166.9
V5 g1: -32.06

Do any of my voltages look out of whack?

Thank you!
Lou