Quote from: J M Fahey on September 05, 2009, 01:03:03 PM
Hi Phil. Those old transformers *did* have a built-in gap, even if apparently it was not there.
To begin with, the EI lamination was *not* interlaced, as in "regular" transformers, but had all "E"s facing the same side, and all "I"s together closing the magnetic circuit. This already provides a usable gap, simply because of die cutting defects and irregularities. To this some added a single sheet of paper (regular printer paper will do) which becomes invisible after varnish impregnation.
For *mechanical* mounting reasons, the first and last E/I laminations were interlaced, simply to act as clamps enclosing the others.
Thus, on visual inspection the transformer looks exactly as an ungapped one, it can be only seen by dismounting it.

Hi JMF,
          Looks like I owe you a chip point or two
Yes I pulled some OTr's apart today and just as you say the *Lams* are arranged to make the gap.
Though no paper shim in the two OT's I've pulled apart?
Never the less there must be some low power point where this *Gap* is not an issue?

I'm sure you can understand my reason for persuing such an idea.
*If* almost any small Mains Tr can be used as an OT (Cheap and easy to source) and powered from the likes of a computer style SMPS (a lot deliver ~about~ 20VDC).
Then the cost is dramaticaly reduced to the point where anyone could build a small 1/2 watt Amp for very little outlay.
Hey this is a SS forum and a lot of *Chipamps* so I'm just trying to add something a little different.
At the moment it's only a novilty but with the right minds working on it I feel it may have merit.
Thanks for the help :tu:
Joe mentioned Dalington but I've had little success with those.
The circuit I've tried seems to have the highest output due (I think?) to the bootstraping effect but the distortion is huge. sounds Kinda nice going through the transformer but I'd like to have some clean headroom before I post a working unit. Phil

I have been messing around with transformer coupling Again :loco

It would seem that the OT imp matching is not over critical in fact I'm getting better perfomance using
a *Mains Tr*
This particular unit is a 240volt pri /25 volt secondary. Simply connect the pri side to the output transistor and connect your speaker to the 25 volt secondary. :tu:

I think the main problem with my circuit (Schematic on previous post) is the signal can't swing negitive on Q2, causing excessive distortion but as it has to pass through a transformer anyway then any high freq hash is wiped off and it does sound quite smooth
even though it is heavily distorting.

If you replace the OT with a droping resistor and Cap couple the output you loose power and it sounds like a very  bad Amp. (which is what it is of course)
I guess it just shows that even a badly designed circuit can be sonically improved via the use of a Transformer.
I'll have another go at it sometime soon but one has to find the time.

*Enzo* asked way back about the OT GAP For SE Amps;

I don't know how far you can push the boundries but I DO Know that MANY of those old Valve radio gram units from the 50/60's used SE OTr's with no gaps.
From what I've read the DC current (which is what will kill it) would not be high enough to cause problems. Most of those old valve units only pumped out about 5 watts at best but over that you would certainly need to consider it.

The only reason I've been messing with this circuit is the possible use as a pedal.
Just useing a voltage divider off the output and send it off to a big amp.
Have fun, Phil.

Hi 93greenstrat,
As it happens I've got one in my shed right now and the owner is wanting it tweaked up.

One big design flaw that was immediatly obvious was the brute force approach to derive the low voltage rails. The board on this one is almost black from the stupid amount of heat dissapated by R 172, 173, 160, 161
and Zeners, CR56/57.
The R's can probably hack the heat but should be *Raised well above the PCB* so the tracks don't get delaminated. This Heat dissapation oversight seems to be quite common even in big name Amps,,, makes you wonder how much they know??
I'm not so sure about the Zeners,, even though they are likely 5Watt devices At such elevated temp they will likely stuff up prematurely as well.

I have never understood WHY makers insist on running commponents at such elevated heat when there is no need to?
At a guess *Two 10 Watt 470 Ohm resistors* would probably work far better,, others here are better qualified and will likely know the right value off the top of there heads.

All the preamps and the switching circuits are powered via the 16 volt rails and dodgy regulation could be the cause of phantom switching and other ill's you describe.

The Valve you mention is powered from the 40 volt rail via a drop across 3 x 470R 5 watt resistors,, they also run quite warm but nowhere near as HOT as the others.
So I doubt that would be an issue.

One other major design flaw I noted is the *Extention speaker jack* on the back panel. Upon insertion of a plug it *Also* lifts R90 off ground and activates C49.
The problem is the *Switch* (mounted on the socket itself) it could actually intermitantly bridge the HOT Speaker output back to R90.
(I noted a blob of Factory goob to help isolate the problem terminals ,,obviously Fender where aware of it)

I fixed this potential hazard while tweaking the tone by simply cutting the *Red and Black* wires from the circuit. The whole silly trick does very little anyway and leaving it out will (ever so slightly) boost the output.  

I'm only tweaking the *tone* on this unit but all my observations will get relayed to the owner,,, and he can then decide whether to sell it or overhaul it before it gives him more grief.

I don't know what tone you're chasing but this owner want's the horrendous excess treble ripped out. My fix was to *Add* a 470pF at C47. I left the original 22pF in place and It did change the amp in dramatic fashion.
(you don't have to pull out the main board to do this trick :tu:)
He has already changed the speaker to a much more civilised mellow unit which I gave him some months back.

Yes Joecools idea of replacing pot will work wonders,, I've never had much success with cleaners,, ie, you have to pull the darn thing apart to clean them,,, then do it all again a few months later to replace them,,, twice the work plus the extra cost of a can of cleaning fluid??

I've only been inside this amp for 2 hours so there may well be other things wrong that I have not noticed Yet. Sadly without a "scope and sig-gen" and all the other fancy gear I won't see all potential issues.
Hope it helps you out a bit,
Phil.

Quote from: J M Fahey on August 24, 2009, 01:22:28 PM
Hi Phil/Phatt
Absolutely spot-on.
Anyway, *for Fender at least*, as you stated, "A" is Log, "B" is linear, and "C" is anti-log.
In Argentina an old convention stated C1=linear, C2=log and very-difficult-to-get C3 meant anti-log, "C" meaning "curve".
------
For example I had "S" curve pots made, the ones used in graphic equalizers, which start as log, have a middle linear section and end in antilog, in practice beind "ABC" :duh , by paying for 500 "tracks" (inexpensive) and having 100 unit lots assembled (regular price), which was very affordable.
------
Unfortunately, the last Argentine factory which used to accept (grumbling) my "crazy demands" such as this, closed on the 2001 crisis.
The owner and his son had been running it alone (no workforce) for the last 5 years and they tired of the endless struggle.
Oh well.
This so-called  "globalization" which really means the renaissance of slavery as a dominant economic force  is killing us all.

Wow JM Fahey, you've been around, 8|
But as you say global pressure forces us to now except second rate stuff which is very sad but not much one can do about it.

I scrounge now for old bits of electronic junk as I quite often find at least one decent component inside. As a hobby type guy I can only access what is on the shelf and the quality of such stuff is just Sad   Out of 15 NEW stomp switches I've had to replace 7 in the last 3 years due to cheap design,, yet some really old pedals made in the 60's are still working.

Cheers, Phil.

Thanks JM,,,
You have a much better way with words. :tu:
I just tend to blab it out but hey we would all bore each other to death if we all felt the same way and there would be nothing left to talk about.
Yes,, giosmrbig  did ask if it was hybrid and I was just warning of the overuse of slick terms.

But alas I have to admit I'm not very impressed with transtube era Peavy's.
I agree some Peavy gear is brilliant,, some of those older bass rigs where quite stunning. Considering the age of the ones I'm thinking of ,, heck a graphic EQ and BiAmp option was ahead of it's time. :tu:

Hey va3ux, Yep ok by me,,, each to there own  :tu:
I have a mate who purchased two bandits some years back and he regrets not doing more research before purchasing. This particular player is a fulltime working guitarist so I do tend to listern to the feedback from these guys over bedroom guitar players (like me )
I've tweaked one of his bandits with so-so results,,ie, still not perfect but it did improve it.
He now also uses my PhAbb semi passive Tone box which helps it a lot.

My general thoughts on all the modern stuff (Valves too)
*They try to do to much in one Amplifier package*

Extreme in the case of the Trademark 60 where the bright button is just plain stupid on channel one.
Yep my other good mate owns one of them ,,
He Thought he liked it but now he hates it.
Trademark 60 is a pain to work on (surface mount double sided board)
But I did find my way through it in the end and I was able to bypass the whole 2 Ch preamp section therby allowing *External* access to the main tone Reverb section and power amp chip.

He now uses my dedicated tone box and Reamp setup and the Trademark 60 is just the final tonal adjustment before the speaker.
The original speaker was also replaced with something a lot less harsh.

Bare in mind these guys are not into heavy metal thrash power chord stuff.
So if that is your bag then a lot of my opinions no just make that *options* are based on the classic rock sounds.

OK I'm an old fart but I think you will find that a lot of the newer sounds are drawn from the basic rock sound anyway.
ie, get the good old crunch rock sound *First* THEN just re EQ it all and bingo you may find a brilliant Metal thrash.

In my somewhat limited experience I've found it much easier to work with speakers that are not so harsh and concentrate on the circuit and EQ,, sure you need more power to get to the same SPL but hey SState power is cheap anyway.

SPL;
Not so important with SS but the old valve amps relyed on power tube distortion a lot and the mistake that was often made by owners of 40 watt tube amps was to purchase 100watt plus gear thinking that would get a louder sound. (cut through so to speak)
often A bitter dissapointment as the big tube amps (although louder) did not sweeten as easy because they stayed clean untill they where stupidly loud.

They would be far better served by just purchasing another 40 watt tube amp,,, thereby moving more AIR and attaining a bigger sound but with the same sweetness of the smaller amps.

If you only play small time gigs or at home then a bandit is gonna sound ok but if you intend to go on the road then do some serious homework before you part with your money as the poor old bandit is going to sound rather bland when it's up against serious pro gear. Simulating the bandit shows up the weakness in the tone stack setup ,,, you are lucky to get 10 Db cut in the mid range and with the dist engaged there is just not enough control.   scratchy fizzy distortion.  As my Bandit friend found out the moment I plugged my tone box in front of his Amp,,, WOW Real bass, real mid cut control. It made the bandit's tone controls sound like they where not working at all.  Arrh I better shut up now because I'm just going to sound like I'm bragging.  0:)All this is just MHO and someone may find some use of it.
Cheers all, Phil.

Quote from: Brymus on August 19, 2009, 03:42:52 PM

Quote from: phatt on August 18, 2009, 10:44:42 AM
Hi posegate,
                Would be better if you just explain the symtoms you have noticed
and then you might get closer to fixing the problems you are having.
Cheers Phil.

Hi phatt sorry to hijack thread but are you ZP? zaphoid phil from Canada?
If so you have helped me in other forums 

Sorry not me,, I live in Australia, 'an I've never been OS,, but hell yeah Canada sounds/ looks like a nice place to live.
Phil.

Hi Joe ,, Quick Q if I may;
Can I enter something on a bread board? With a schematic of course and maybe a short sound clip if I can get that to all happen.
Thanks,, Phil.

Hi J M Fahey, Wayne,

AFAIK,
         That *C*would indicate an *Older type*Audio taper pot.
I don't think you can get them anymore,, probably just fender using up old stock.
Anti-log would be an *F* in the old Format,, I have no idea what they call anti-log now?

Old Code;
Lin = A
Log = C
Anti-log =F

New Code;
Lin = B
Log =A

I'm in Australia,, I don't know if other countries have different codes but there used to be a *G* and *D* taper as well. 
Yep it Can get very confusing to say the least. :duh

What is labeled a Log Audio Taper *Today* is very much different to what was sold 40 years ago. I ran into this issue while I was building my *Tone Boxes* Where it finally dawned on me that the Original HiWatt Tone stacks *Only Work* correctly with the *Older type* 500k Log pots. The new ones just don't have the magic curve shape.

BTW those 16 mm pots are quite prone to stuff up especially if they are PCB mounted.
Wanye,,, Go with JM Fahey's advice as the Frontman circuit is not Taper critical.
Phil.

Hi posegate,
                 Would be better if you just explain the symtoms you have noticed
and then you might get closer to fixing the problems you are having.
Cheers Phil.

Hi ,,
Transtube means nothing it is just an advertising gimick to fool the novice,,
*It is all SState*. Hybrid usually means tubes and SState combined.
Sadly anything with the words *tube* or *Valve* mingled into the front panel blab will SELL.

Take the famous TS9,,, Tube Screamer pedal ,,, hum notice the use of the *tube* word?
To it's credit it did at least wipe off a lot of treble which went some way closer to an overdriven tube sound,,, but not a tube anywhere inside.

Bandits/studios / pros they are all very similar (ie transtube teck) and some folks love them to death but IMHO there are far better amps out there.
Don't buy one if you are chasing a mellow sound.
Cheers Phil.

I second joecool,,
adding if no experience with electronic gear don't go near it until it has been checked by a certified electrician or just take it to a repair shop. This is no joke, you could be flirting with something very dangerous.
Phil.

Hi Zappacat, still struggling with it,, oh dear Hopefully I won't add to the confusion.
JMFahey has explained it well but there maybe some confusion about ground.
The common or ground if you like is the CT (Center Tap) of the 15/0/15 winding.

So *0* in a 15/0/15 secondary is *Common* to the Two 15 windings.
So using the same explaination as Fahey, taps 1/2/3 equal 15/0/15
In most amp circuits the *Common* CT becomes the *Ground* of a split supply.
Another way to express the same winding would be to say; 30 volt CT.
Or a single 30volt winding with a Cent Tap.

You should set your DMM to read AC Volts and be able to get a reading of ~30 VAC between tap 1 and 3.
Which should also give you ~15VAC between (1 and 2) or (3 and 2).

If you are doing everything right and you can only get low readings as you have shown then it's probably blown.

The faint click or whatever is likely due to the couple of volts generated via magnetic coupling, even though the wire has gone open circuit it still induces a small voltage due to magnetic coupling of what is left of the windings but nowhere near enough to power up.
ie, a small voltage with no current capability hence the power indicator light won't even light up.

No you don't need the transformer connected to the circuit board to get the AC readings of the transformer.
Sound like a new one is needed. Phil.

Hello sergscar,

Well your Father in law must have a cosmic connection because the AVA100 is indeed using a cake tin,,, we call them *Lamington trays* in Australia. :loco

http://ozvalveamps.elands.com/ava100/ava101lamington.htm

Note this Tube Amp is built using cheap transformers,, as you don't need special OT's ,, this thing comes in at a very low cost.
I think the most expensive part is the OT , under $20 Aust.
If you want to see the *OT Trick* find the artical on *Using Line Transformers as Output Transformers*

BTW,, AVA or ANZ site is dedicated to Aussie and New Zealand Valve Amps that have been built over the years. just about every Amp built and sold is on this site.
Pages of useful *how to DIY it all.*

A couple of my circuit ideas are also on these pages,,, have a look under *Reverbs* and you will find comments on my *Maxiverb* stand alone reverb unit
Enjoy,,, Phil.

I'm with Enzo on this,,, good advice :tu:

JM Fahey you seem to have a nose for sniffing out those Schematics,,, good on you.
Interesting as the input section is almost identical to the *Rock Pro* and or *Perfomer 1000*. A friend of mine has the 1000 and he is not happy even though he bought it on the basis that it had a Valve inside it.
Phil.

Quote from: sergscar on August 05, 2009, 03:07:49 PM
Hi J M,
Thanks your wise advice. I'll, then, use 01 x EL84. Frankly speaking, I used the "wrong" rule that says... the more expensive should be better... but seems to be this is not the case.

About the Chassis, please don't laught (well, you can, but not so louder, please...  :duh ) but i'm going to try a very unusual material for my first try. Here it goes my crazy idea:

Imagine a regular 12" x 16" x 2" (H) alluminium's roasting tray (those you use to cook delicious turkeys...),
turn it upside down..., and proceed marking and drilling as per your project.
The one I'm going to use have some small "flaps", which I can cut out and file without much effort.



I guess the alluminium thickness is strong enough for supporting the transformer's weight, so I though... why not to give this mat a chance ?

Do you think it may work ? I'll chase the right measurement tray and post a picture.
Obviously, after I start to do the job, will post a "how to" for our forum's friends !

Sergio

P.S.: My wife is a little worried by seeing me so interested in "her" kitchen's mats... She knows me very well !

Have you been looking at the AVA 100 project where a chap built a whole tube amp on a baking dish?
Yes it has merit but not the kind of amplifier you can take to a big gig.
The pan needs to be screwed down to a solid base.

Re Cost of Single ended tube amps;
It might seem at first to be cheaper/easier to make SE....
BUT! remember PP (Push Pull)  OT's (Output Transformers) are easier to source.
with PP you can use a line transformer for a small 10 watt amp very cheap.
Phil.