First time #183 Build

[MusicMaker]

Welcome to TAG.

This is probably a good time to talk about speakers. Conventional wisdom splits down the middle. One branch likes heavy, cast-frame American drivers like the EVM12L (or S), Altec 417 and some of the Eminence line. The other branch favors Celestions -- particularly the G12-65 or Scumbacks/WGS speakers from that lineage.

Me; I have a set of both and would hate to have to choose permanently.

Spend some time researching the speakers and cabs that work for the sound in your head. There are a lot of 183 clips on YouTube. Many of them describe the box under the head.

Also keep in mind these amps don't favor all guitars equally. Strats don't get a lot of love with the later generations of the ODS. The 183 is towards the end of that line. At least, a lot of us try once and then get a Tele or something with buckers.

The last thing to add to your to-do list is whether you've considered whether building a matching active loop. It is a one-tube FX circuit that adds a lot to the sound whether you actually use it for effects or not. The jury is out as to whether you must have one but it you have one resistor left in the bin when you finish the amp, you'll need to do something with it, right?

Skip

Thanks for the welcome!

I have an 1963 Epiphone E230TD Casino I play. I hope that works? The finish got moisture damage (nitrocellulose doesn't like H2O) I haven't figured out how to rectify. It looks like it's just the clear coat. The red is still apparent. It has a P90 neck and a retrofit humbucker at the bridge.

and how did you know I have one resistor left? It's a 47 ohm. I scoured the scheme and it's nowhere on there! Not sure where it goes.

Sounds like you're describing the Dumbleator?


Speakers is a great subject. I'll check out the youtube clips.

I ripped two 12's out of a SUNN half stack my brother gave me. They've been stored in the basement for 20 years or so? I might give one of those a try, though I'm not sure they can handle a Dumble clone? They're 60w rms each.

see pics

My plan was to make this a head, then a single 12 cabinet in the Dumble style to split up the weight issue.

[MusicMaker]

The progress so far. Finished the heater wires. Installed the 5W resistors.

[Luthierwnc]

Yup, the Dumbleator.

Our own Boldaslove has a number of 183 with loop clips on YouTube. Worth a look. sh

[MusicMaker]

Just curious if anyone uses an O-scope to set these amps up?

If so, any recommendations on brand? I've seen the 'PC based' and wondered if they're worth considering? Bench models like Tektronix and HP have a better reputation.

Used are fairly inexpensive $150 to $300 or so. Lots of 100Mhz models.

Any recommendations or warnings?

[Structo]

I use a scope not so much for setup but as a diagnostic tool when there are problems in the amp.

Best setup tip is to play the amp for a few days before you decide to change something.

Lots of knobs to adjust.

[MusicMaker]

I got the email that the iron is on its way!


I've been reading up on tubes.

AmplifiedParts.com has a nice page on 12AX7 Comparison of Current Made Tubes here:

https://www.amplifiedparts.com/tech_cor ... made_tubes

There's only 23 to choose from!

EL34's have several iterations as well.

I'm overwhelmed at the choices and instead of just buying a set, I'd like to learn why anyone chooses a particular brand of tube over another?


In lieu of prior experience with this or that tube, what criteria do you use?

[MusicMaker]

Just received the trannies today. 10 days as suggested.

22lbs.

Still reading about tubes.


Thinking of getting the Marshall EL345050 set because it comes with an extra 12AX7 for a dumbleator.

[Structo]

Unless you have some vintage preamp tubes, then you have to decide what brand of current production tubes you want to use.

That chart of the various brands can be used as a guide, but you can't beat
plugging the tube in and listening to it.

I find the JJ 12ax7 is kind of a neutral sounding tube.
Not too bright but it can help tame a bright amp.

I find the EH 12ax7 to be on the brighter side that I probably wouldn't run as a V1 unless the amp was very dark to begin with.

I had a couple of Chinese Select HG 12ax7's that sounded great in a higher gain amp.

You can have the same brand, the same designation and they can sound different due to current demands and gain.
This is the life of analog.

I haven't tried many of the New Sensor stuff, like the Mullard, Tung Sol, etc., and I believe you are probably throwing dollars at a tube with an old trade name to entice you to buy it.

On the other hand if you are diligent in searching, you can find vintage preamp tubes that still have a lot of life left in them.

These are mostly pulls, taken from vintage equipment like organs and other tube related gear.
Best sellers will post the test results from tube testers.
Many will be top tier tubes, re-branded for the company that used them, such as Baldwin, Hammond, etc.

Tubes like Sylvania and Raytheon, General Electric, RCA; Simply have a different name on them but are the same tube.

The 1960's GE short plate 12ax7 is the one I use most.

Here is another tube guide.
http://ampgarage.com/forum/viewtopic.php?t=17936

[MusicMaker]

Thanks! I've been reading and watching videos. That link in particular.

Even found one where the guy makes his own!

I have a line on 2 Wurlitzer 12AX7s. Shiny black long plates.


What would be the best placement V1 & V2, V2 & V3, or just one of these with something else for the other 2?

My reading suggests for high gain that the short plate valve is better - these are long.

One problem I've run into with the microswitch under the toggles is it tends to drop out of the chip holder at the slightest bump. Not good. I was considering flashing some solder on the pins to thicken them.

Anyone have a better fix?

TIA

[MusicMaker]

Well, I have it all put together.

Between work and play and getting some time to get my head back into the schematic and wiring I think it's done.

My next project is building the light bulb current limiter and testing it.

I used Ceriatone's layout. I also consulted the Albany/Quinn layout for the convenience outlet. I searched high and low to find a receptacle like theirs, but to no avail. In the end I visited my local electronic junkyard and found the 'mate' to the computer style plug. I happened to have an old monitor chord from the days when you'd plug the monitor into the back of the computer, so it will power the D'lator when I get around to building it.

Looking back on the process I would have to say I made a few mistakes, but errors in assembly that, had I studied more photos I might have avoided. The 5w resistor location for example. I ended up moving it off the back of the socket because it was a bear trying to solder that! Fortunately, I was able to reverse and correct them without too much trouble. Routing some of the wires (B5 plate) from the bias board might still be 'problematic' because Nik's board isn't exactly like HAD's design. I just made a bee line to the 150K and 220K under the board. It's 90 degrees to nearly all the wires and components.

I'm considering using the Full/Half power switch. If I understand the wiring (from Albany/Quinn layout) it merely shunts the cathode of pin 8 of V4 and V7 to ground. When it's “on half” power the LED lights to remind you where it's at. Unless I have it backwards? I haven't wired it as of yet. I need to get two 10K resistors.

I've yet to order the glass. I was getting 'lost' in all the “BS” about OS vs NOS. 'Jee, do I really need original RCA glass for $158...each??' I really don't need a 1945 Domaines Barons de Rothschild Chateau Lafite Rothschild bottle of wine for $800, when a more recent vintage would suffice. I think the EH and JJ's will suit my purposes just fine until I become rich and famous.

I might even scour the local electronic junkyard (though I believe it's been picked through over the years.) I did find a Sylvania and an original RCA 12AX7 for $5 a piece! Don't know if they are good, but for that price I took the chance. Their tube tester machine was on the fritz! There's rows upon rows of old glass. Probably for TV's is my guess? Who knows? I might get lucky! Heck, after poking around there I could probably source another build from what they have!

My background is in data networking and as I was twisting the AC wires it came to me that this is done to reduce the magnetic lines of flux that would radiate off a straight wire. The 'right-hand rule' applies and the twist acts like an inductor to AC. Same thing for 'twisted pair' Cat 5 wire. There's an algorithm used to eliminate crosstalk on data wires and each pair has a unique twist to the rest in the sheath. It gets pretty involved, but anyone interested can look it up.

Next up - after testing the build is to make a box to install the head. I suspect that will take a couple of weeks planning, cutting, and assembling.

If you don't all mind checking the pics to see if I missed anything, I'd appreciate a 2nd pair of eyes looking over the work. Thanks!

I plan on using Paul Ruby's 'First Powerup' to guide me. I'll have to desolder a few things first.

http://www.paulrubyamps.com/info.html#FirstPowerUp

[MusicMaker]

A few more pics

[MusicMaker]

Valve wiring

[Structo]

Looking good there!

As a fairly complex amp to build it's easy to miss things or even mis-wire
something.

A good thing to do is walk away from it for a day or so, come back and check it over again.

Paul Ruby's start up guide is a safe way to start the amp the first time.
A bit complex and you have to unhook some wires.

But using the bulb limiter achieves almost the same thing by checking for excessive current draw, like a short circuit or wrong wire connection.

I would first measure the power supply voltages without tubes plugged in.
Check plate voltages (they will be higher due to no loading.)

You can start with a 25w or 40w light bulb and it limits the current to the amp.
On power up the reservoir caps charge and after a brief flash (main caps charge) then the glow will lessen.
Flip it off standby, it should brighten momentarily again then go to a lower glow.
If it stays bright, there is a problem.
If you really want to be sure, then step up to a 60 watt bulb.

OK plug tubes in and try it again.
Remember anytime you power up a tube amp with power tubes installed, you must have a speaker load or dummy load connected to the speaker output.
Measure some voltages now that a load is on the PT.

If that all checks out, plug in the speaker and guitar and make some noise!

[norburybrook]

looking good from my amateur perspective

after building one of these type of amps most other amps will seem very simple afterwards

I built #102 this year and it was a great learning experience.


I've started a 100w bluesmaster recently ..........................................


Marcus

[Guitarman18]

MusicMaker,

Your build looks good. I'm not sure if anyone else has mentioned it but I would have to say that your mains IEC socket is the wrong one for that application if you are using it to receive the mains. If it is to daisy chain the mains to other gear then please ignore my post!

Edit: I've just spotted the grey mains cable with strain relief entering the chassis from underneath. Apologies if I caused any panic!!


Just trying to help.

Good luck,

Paul.