transformer questions

[Speakz]

Thoughts on brands of transformers?  I was also curious about the ones doug sells here, I didn't see much description about their make etc... so any help there would be great.
Right now I'm leaning toward vibrolux transformers for my single channel AB763 but was also curious about the super reverb output transformer.  I'm planning for a weber 12F150 or C12N for this setup.  Would the super transformers be too much output for 1 C12n style speaker?

Thanks     

[sluckey]

Would the super transformers be too much output for 1 C12n style speaker?

The OT expects to see a 2Ω load. That's typically four 8Ω speakers in parallel. It would be a poor selection for a single C12n (unless you have a 2Ω speaker).

[Speakz]

So does a C12N style speaker sound better with a particular impedance?

[HotBluePlates]

So does a C12N style speaker sound better with a particular impedance?

A C12N is an 8Ω speaker (as far as I've seen). If you plan on using only one, then you have an 8Ω speaker load.

In order for the amp's output stage to operate as-designed, you need to attach a speaker load which is numerically-equal to the output transformer tap you're using. So that 8Ω speaker gets attached to the 8Ω tap.

Thoughts on brands of transformers?

I pretty much pick the one which has the specs I need. I don't worry about brands too much.

[Speakz]

it looks like Jensen does make a 4,6, and 8 ohm C12N and Weber does the 12F150 that way as well.  If the Vibrolux transformer is a 4k primary and 4ohm secondary then the speaker output would 4 for both correct? other transformers seem to change when new speakers are added.. amI missing something?

[sluckey]

amI missing something?

Maybe. You originally asked a specific question about the Super Reverb transformer that Doug sells. Now you are talking about a Vibrolux OT. The two OTs are not the same. And it's because the amps have a different speaker configuration.

[HotBluePlates]

it looks like Jensen does make a 4,6, and 8 ohm C12N ...

Thanks, I overlooked that.

[Speakz]

Yes I'm asking multiple questions at once.  I've owned and played a '71 Super but it was too heavy to lug around to clubs.  Also, over the years 6L6's and the C12N type speaker are two components of overall tone that I want but weight rules out the bigger amps for me. 

Are there some specific things to understand about PT and OT together.  I see Heyboer makes: 

HY018343    $68.00    40    Multitap output transformer for general purpose use.  4K Primary, 2-4-8 ohm secondary, larger size similar to HY022855.
     
Could/should I use a vibro or super power transformer with this?

I'm at the point now where I have to decide on the transformers to order the chassis.

[Speakz]

I appreciate your help and input.  Even though I've read a couple books this still feels a little paint by number at times lol... 

[HotBluePlates]

Could/should I use a vibro or super power transformer with this?

I'm at the point now where I have to decide on the transformers to order the chassis.

Either the cart is before the horse, or you're not telling us everything on your mind...

The first question I'd have is, "What amp are you wanting to build?" Because most commonly available big parts (like transformers) exist because there are already many amps which use them, it stands to reason you'll be making something "similar-enough" to some other existing amp.

So what is the amp you're trying to build? Knowing that, parts are easy to select.

[Speakz]

Sure thing...  I'm building the single channel AB763 blackface circuit and am now trying to decide which transformers are appropriate to run the circuit at 30-40 watts, with 6L6's, as a 1x12 combo and the potential to run an extension cab of another 1x12 if need be.

If you were building this format which transformers would you choose?    

[HotBluePlates]

I'm building the single channel AB763 blackface circuit ... at 30-40 watts, with 6L6's, as a 1x12 combo and the potential to run an extension cab of another 1x12 if need be.

If you look in Hoffman's store, there is an output transformer described as "40 watt 2 6l6 2-4-8 ohm output." That's the part for you, as it will be a 4kΩ primary, and gives the option of several output impedances. Since you'll use a 1x12 most of the time, you'll probably use an 8Ω speaker on the 8Ω tap.

If you give yourself an impedance switch ahead of the (pair of) speaker jacks, then you can switch to the 4Ω tap and add the 2nd 1x12 cabinet as needed.

As for the power transformer, any one suited for a 2x 6L6 AB763 amp will do. Hoffman carries the Part number 022798, which as the catalog says is suitable for a blackface Bassman, Pro Reverb, Super Reveb, Bandmaster, etc which all had 2x 6L6's. By this point in the 60's, Fenderr largely had a single preamp circuit, and amp models mostly varied on effects or not, specifics on channels (like Mid controls) and size/number of speakers.

[sluckey]

I'd use these...

• 40 watt 2 6l6 2-4-8 ohm output
• Power trans Bassman super rev
• Large Fender choke
• Reverb transformer Fender

Available here...
http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Transformers&ORDER_ID=!ORDERID!

[Speakz]

Thank you both...  I will go ahead and order those.  2 follow up questions... 

1.  Do you think there would be any problem fitting them onto a Princeton reverb chassis?

2.  HBluePlates do you know a of a wiring diagram or schematic that shows how to hook up an impedance switch ahead of the jack as you describe?     

[sluckey]

1.  Do you think there would be any problem fitting them onto a Princeton reverb chassis?

Yes

...schematic that shows how to hook up an impedance switch ahead of the jack...

Here's a schematic for my switch that I got from Hoffman...

     http://home.comcast.net/~seluckey/amps/18w/18w.pdf

[eleventeen]

You'll probably need some more "advanced" (for want of a better term) building chops to throw that transformer complement into a Princeton Reverb cabinet AND onto a PR chassis ESPECIALLY if you decide to go to a 12" speaker. It is very possible that the OT will interfere with the speaker magnet or frame. I have built a "Bassman/Pro/Super" (eg; 2 x 6L6 power) into a SF PR cabinet. Now, I used an Altec 417-8H speaker I had laying around which has a VERY DEEP spider on the speaker and a LARGE magnet ass'y. I had to rotate the speaker some (about an inch) such that the OT (centrally-mounted) pokes into the space between two spokes on the speaker. That, of course, meant redrilling the speaker baffle board (unless it's OK to have holes drilled thru your grill cloth = ugly) and you can't really do that without removing the grill cloth. And...you may decide that after you saw out the bigger hole for the 12" speaker, the baffle board is not structurally sound any more because the cutout hole comes too close to the edges. (I did both of these 30 years ago, when these amps were cheap and common, so please excuse me if if I am hazy on some details) Or it could mean making a whole new baffle board out of good plywood, which is what I did.

Another amp I built was a 6L6 fired amp in a Deluxe Reverb cabinet/chassis...on that one, I had to move the output transformer to the end of the chassis opposite to the power tranny and splice and run all the OT leads across the top surface of the chassis in a bundle...that one used a JBL D-120-something speaker which is NOT a deep spider/deep magnet but it DOES have a THICK mounting ring but I STILL had to move the output tranny (which was an OT from a Dyna 35-watt mono amp which is a SMALLER tranny than a Bassman/Super but not a Pro. Both of these "hotrod" mods (which is what they were, of existing amps) used SS rectifiers.

I can almost guarantee you will not have room for the big choke without moving the OT.

It's all completely doable, but it ain't snap-together by any means and it's definitely extra work. Be prepared for weird interferences, esp if you go a 12" speaker in a PR. Remember, anything you mount on the chassis has to mounted about an inch back from the edge of the chassis where the controls poke out, the front edge. Otherwise, the chassis will not slide over the baffle board. This is most critical on the power tranny upgrade. Before you take the existing amp apart, take a sharpie or a pencil and draw a line on the chassis against the back side of the baffle board where it meets the chassis. This is your "do not exceed" line and if you further wrap the grill cloth around the back side of the baffle board, you will lose another 1/8" or so. It's also possible that the chassis-mounting nut that is in the front corner behind the new power transformer (near the pilot lamp) will be INCREDIBLY hard to get to and you may have to make something out of some rubber hose or a piece of jacketing from some cable that will let you poke that nut up and into the amp so that the chassis-mount bolt can engage the threads.

[HotBluePlates]

1.  Do you think there would be any problem fitting them onto a Princeton reverb chassis?

As one who's been where you are now...

Expect (many) unforeseen problems in your early builds.

If you build something that departs from dead-stock, where all the details are conveniently worked out for you by others, or if you try to cram in every bright idea into an early build, add an exponent to the number of problems mentioned above.

You will surely (just like I did) make some silly errors during your build. If you change the standard layout geometry (40w of 6L6 in a 18w Princeton package, with a 12" where a 10" goes, etc) you will find yourself having to make unplanned changes to get things to fit. And then you will have to make more changes to compensate for the changes just made where you had no choice, and things spiral away...

But I don't say that because I've done exactly that and abandoned a build that I found out could not work, after getting 65% of the way through the build... Oh wait, that is exactly what I did. 

I'm not certain, but *I think* you can fit the 6L6 transformers in a Deluxe Reverb cabinet/chassis (which is also already sized for a 12" speaker). However, you will want to verify with some well laid out chassis diagrams and transformer mounting specs.

[Willabe]

1.  Do you think there would be any problem fitting them onto a Princeton reverb chassis?

Yes!

Listen to Slucky, HBP and 11teen, don't use a Princeton Reverb chassis for this build with the 6L6 PT/OT/choke.

Get at least a few builds under your belt before you try to jamb a bigger amp (which is what you are wanting to do) into a smaller chassis. Even then it might not work.

Many guys who build a Champ type amp or a Tweed Deluxe 5E3 amp for the 1st time have problems with their  - lead dress- even with a stock clone chassis and eyelet board.

I think HBP's right that a Deluxe Reverb chassis might work but you'd have to enlarge the PT cut out, then make the larger OT fit - AND -make the choke fit which a PR doesn't have. Those 3 larger pieces of iron wont fit on a PR chassis.      

Also because you want a single channel AB763 if you buy a clone chassis you'd still have a problem with the clone chassis as drilled - unless - you find 1 that is drilled for a single channel.

Do you plan to have the AB763 reverb and trem?

            
              Brad        

  

[eleventeen]

"Be prepared for weird interferences, esp if you go a 12" speaker in a PR."

I just wanted to amplify (no pun intended) this statement. In fact, it's impossible. There is in fact no comprehensive way you can prepare for the odd interferences the fat tranny set plus a 12" speaker will create....without actually building it. And as HBP said, it's entirely possible you can get yourself into a situation where you've driven into a blind alley and can not make it happen.....at least with what you know and can execute.

I don't want to discourage anyone from trying anything they want to, but all of us have and have seen projects that sat on somebody's shelf, sometimes our own, and sometimes a fellow amp-builder, for 5+ years until they gave up on it, and this could be that for you.

This is not a good path/choice for a first project, IMHO. If you ONLY want to do the trannies & go with 6L6, fine. The bigger speaker, if I recall correctly, will be the source of several problems, and I humbly suggest that you are probably underestimating the complications. The reason, again, if I recall correctly, is that a 12" speaker in a PR cabinet has *exactly* one place it can go, position wise, with almost zero slop possible in terms of where it is mounted. Talking maybe 1/8"-1/4" of variance. Therefore *everything else* has to allow for where that speaker goes, including how it is rotated. It's also possible that a speaker whose frame has 6 spokes instead of four won't allow the OT to be mounted in the center of the amp and will force you to move the OT farther from the PT. Of course, if you are not prepared for that...then you have to redrill the mounting holes for the new positioning (and those holes are pretty close to the parts board so that has to be done most carefully) but >>if you have to to redrill the (BIG) hole(s) the wires pass through because the OT will not mount in the center, you'll almost certainly have to remove the parts board from the amp<<.....after it's been wired up..........right? That would unquestionably suck.

The Altec I had has 4 spokes and was cast, not stamped so there was lots of room between the spokes, and they were narrow, so there was "lots" (ha) of room between the spokes.

Are we used to specifying our speakers by how many spokes are on the frame? Uhhh, no. Usually it's "tone" or "sound" we're after.

You pretty much have to build with the speaker position *and rotation* established first and maybe I am exaggerating and with your particular choice of spkr mounted, you'll be lucky and everything will go just fine.

Just trying to save you some pain. I *have* done this. It *was* aggravating and tricky.

On the positive side, my little hotrod SF Princeton-Rev is one the best sounding amps I've ever owned. (I'm a fan of blackface amps, not really so much tweed or Brit amps)

[Speakz]

Thanks guys glad I kept asking questions.  I'm happy with a Deluxe reverb size cab and chassis. How hard is it to drill the front holes for the pots into the chassis? Is it the same level of work as drilling through stainless steel pots to install ball valves?  Which I have a bit, drill, and oil for.  I was thinking about purchasing one from here:

http://seasidechassisdesign.com/

In which case I would need to drill out the front and any other odd holes.  He said he could cut for the transformers and the tube sockets..?  

To answer Willabe yes I am planning on Reverb and Trem.  Following Doug's directions and parts list minus the switch to F&T Filter Caps.  I may skip the Mid pot but haven't decided yet.

[HotBluePlates]

We've perhaps made an assumption that we shouldn't, so I'll ask: Is this your fist build?

... Deluxe reverb ... chassis. How hard is it to drill the front holes for the pots into the chassis?

Do you want the amp to look like an original Deluxe Reverb? If you notice, those amps have a sloping front face.

I see the pics on  his website of a slope-faced chassis with a blank front panel. In order to drill holes for the pots, you would have to use a hand drill from the outside of the chassis. The space on the other side of that front panel is triangular and has a lip on it, meaning you won't be able to easily brace the chassis from the inside. You'd either need to cut/shape a matching triangular piece of wood to brace the chassis on the inside, or risk a lot of problems getting the holes drilled in the correct spot and perpendicular to the chassis face. That small triangular face also means you can't use a drill press to make the holes (which is how I drill my chassis now).

What does all the above mean? If you want a good-quality result, the chassis maker should already know the control positioning for the amp you're building and drill out all holes prior to bending that front face.

If it were my project, and I planned on building a Fender-clone, I'd buy a Fender-style chassis and faceplates (and maybe cabinet, probably from one vendor) with all the typical holes and cutouts already in place. In fact I did just that when I built my first 5E3 and still hand to do some drilling by hand to mount tube sockets, the circuit board and output transformer.

[ac427v]

Allen amps sells chassis that are like one channel Fender. They do not include face plates though and that can add a significant chunk to the bottom line. Still his amps might help you see how he has dealt with the problems of fitting 6L6 power in a smaller cabinet.

[eleventeen]

Is it your plan to buy, a la carte, a Fender-type cabinet, then to tolex it and buy handle and corners and etc; etc?

Because at some point, it may well pay for you to go find a used Peavey amp, gut it, and do your build inside it.

[Speakz]

I replied then it was lost so hopefully this isn't a repeat post...

11teen:

My plan has been to build this single channel AB763, decide on transformers, order chassis, and then build the cabinet myself fit that chassis.  orginally

I actually have a Peavy Classic 30 currently in the basement which I have modified.  I also have a friend who has a broken classic 30... do you think this format would it? 
Originally I wanted to build this AB763 in the layout of the tweed style similar to a Classic 30 but in black tolex with white piping.

HBP:
Yes this is my first build.  My related experience has been building my own guitar, pedals, and furntiure.  I've also read the blueguitar mods and used those for my classic 30, new caps, reverb tank, and speaker. These have all come out well.  I like to do a lot of research and build in stages.  I tend to read, ask lots of questions, and take my time with it.  My uncle has also built guitars, Ukes and speaker cabs as well as various other things from scratch so I have some in person help as well.  It's the chassis and electronics end that is new to me and him besides soldering together pedals and reading gerald Weber's book and online video's.   

[eleventeen]

The "Classic ---" Peavey amps have value, judging by what the asking prices are on them. Those are all tube amps and I wouldn't gut one for this purpose. My impression is that they have favorable ratings.

I was thinking more along the line of taking a dead SS Peavey amp and gutting it for your cab and chassis. These are often sold on Craigslist for $25 or so, sometimes free. Pacers, Bandits...several other models. I can understand the desire to build stuff and if you have the time, tools, and space, then fine. But buying a (say) Deluxe Reverb cabinet from a clone maker and buying a chassis from Mojo or whomever, then buying the tolex, the handle, the metal corners...well, if your time is worth anything, you could spend $300 worth of it building a tolexed box and getting the sheet metal chassis for a DR. That's before you build anything electronic. Meanwhile, a dead $25 Peavey something-or-other in a cabinet with fitted chassis, handle, and corners puts you far ahead of the game, as I see it, and that's my only point. Yes, you'll have to work some voodoo to make the chassis work, but if you believe my prior posts, you'll have some odd stuff you'll have to do to a DR and especially a PR if you want to end up with a 2 x 6L6 + 12" speaker amp.

[Speakz]

Thanks 11teen.  I'm going to go with a larger chassis as you all have recommended to accommodate the transformers etc... and give me room to work and to separate everything.  That much I've decided and then I'll face the next step after that.

 

[Speakz]

In terms of rectifier would be able to use a GZ34 or a 5UG4 with those transformers? I would need to re-bias correct?

[HotBluePlates]

In terms of rectifier would be able to use a GZ34 or a 5UG4 with those transformers?

The Transformer Info page shows that the #022798 I suggested earlier has a 5v 3A winding, which means it can support either a GZ34 (2A) or 5U4 (3A) rectifier. Or you can use a solid-state rectifier if you like.

I would need to re-bias correct?

If you wanted your tubes to run as hot as possible while still staying safe, you might rebias if you swapped from a GZ34 to a 5U4. I myself probably wouldn't bother unless I saw a tube redplating. I'd probably only check bias when replacing output tubes.

It's funny... on my last amp build, I gave myself the ability to measure each tube's current, and to bias & balance tube current. But I rarely check, and tend to plug n play.

[PRR]

> How hard is it to drill the front holes for the pots into the chassis? Is it the same level of work as drilling through stainless steel pots to install ball valves?

Stainless steel is a royal pain to drill. The Chrome in SS work-hardens when you rub it. Your only hope is a sturdy drill, reasonable speed, and high force, trying to shave-out chips faster than the SS work-hardens.

Common "mild" steel used in older cars and all amp chassis is MUCH easier to cut. You get a 8-pack of bits for $12 at the home store, a 3/8" electric drill, maybe a bit of oil, and just drill. Be careful at the end, it grabs.

Except as HBP is saying, you really want a hardwood block behind the hole, to support the metal against bending, and to catch the bit as it comes through. And on slope-front chassis that can be a real hassle.

I just tested a Milwaukee electrician's step-bit which worked REAL well in a low-price cordless drill, all the way to 7/8" (it goes to 1-1/8" but I wasn't clamped well enuff to risk that). Unfortunately Home Despot seems to have de-listed it. And it was $49 so not a casual buy.

For precision chassis drilling you can't beat a Drill Press with enough table to *clamp* your chassis and blocking. Those clever Chinese dump them in the US market as low as $49.

[Ed_Chambley]

I am late to the party, but If I get what you want to build it is a single channel AB763 with reverb and tremolo,
Bias Vary or Roach?

I will share my experience.  You can use a princeton chassis, but you must pre-plan well.  You would not want to use a princeton cabinet so you will need a custom cabinet.  yes, you can shift the trannys to accomidate certain speakers, but if leter you decide to replace the speaker you will probably have problems.

If you build the cabinet 3" taller everything will work.  That being said, I do not understand why you would want to.  The only reason I did is I had the parts laying around and just built my own cabinet.  You build cabinets too,

I understand people wanting a single channel.  The idea is we don't use the other channel so why use the parts.
BBBBBBBBBBAAAAAAAAAAAAAAAAAAWWWWWWWWWWWWWWWWHHHHHHHHHHHHH!

The amps I prize mostly have 2 channel and were common chassis.  In my fenders both channels have reverb.  I spec one of the channels differently and now I have 2 individual tones for far less money than another amp.

Just a couple of weeks ago I had a build come back and the owner wanted an overdrive.  Sluckey mentioned cascade the normal with the vibrato channel and use an ab box to switch it on.  Real tube overdrive.

Would had been much more difficult with 1 channel.

He needed it quickly and was playing the amp live 3 days later.  Total all the costs of your single channel including labor and hassle for drilling a blank as I am assuming you do not have punches.  

Then look at sourcing a Super Reverb Chassis and build whichever cab you want. Mojotone had Twin Reverb chassis on sale for less than $50, not sure if they still do.  Be careful to insure your cab opening will accommodate the chassis.  You have to have a cab and chassis anyway and how much more are the parts for the other channel and is it really worth saving $30 to drill a chassis and then have to make a custom faceplate?

That being said, maybe you want a single channel.  I do not think it will end up being cheaper unless you already have the chassis with faceplate and correct cabinet on hand.  You can still source your Iron from Hoffman, but be sure to understand his policy on no returns.  I have had Mercury Magnetics and Heyboer replace transformers because they were bad out of the box.

If you were building a square front, tube up like a Marshall Style my opinion would be different and if you already had the chassis and headbox, a custom would be the way to go.

Not trying to throw a Monkey Wrench in, but using the correct chassis and faceplate with the cabinet you want will make an amp that looks like a handwired factory Blackface made in 2014 with less hassle and most likely less cost.

People talk about clones being amateur builds and I have to say some of the guys here have made some very nice custom amps, but the custom can just be in a "large" predrilled chassis.  If I have a AB763 with a fender slant chassis with a black faceplate in a complete combo or a silveface and make them look store bought I am satisfied and tend to just play them.  All my custom builds get experimented with.

Just my 2 cents, thanks for listening.  Your opinion may be different and that is how we get cool things like LED lit Supro Caged heads with a meter on it, but is it also how I get metal boxes with no faceplate with a sharpie V  T  B  M written on them.  Nothing wrong with that either, but that amp is not worth as much to me even if it did cost more.