New old amp day

[Craig]

i'm so glad guitar tones make me feel this way,,

I know, right?

One of my favorite youtubers is Johan Segborn, he just uploaded a clip of a Dynacord Amigo amp.
I love mine.
I guess that'll be the next in my pictorials.

The url failed the urlvoid test (scumware)...so here's the unclickable link-

Code: Select all

https://www.youtube.com/watch?v=6ryc8LPvGRo

Or you could post it as an inline video:



See: Tutorial: Posting YouTube videos.

Hope this helps.

[Crusher]

Stop with the amp porn, I'm a broke man I don't wanna go down that route again But please, don't stop! erh, well... I mean, stop! Wifey said stop! So please, don't stop! I mean stop!!!

Dang that is beautiful.

[Elwood]

Thanks Craig for confirming that's alright, I wasn't sure.

Crusher,
I can't stop 'till I build some from scratch, that's what cured my guitar quests.
(now I crave better and bigger tools).

hehe...glad to have an audience (including your wifey )

[Crusher]

I will never get cured... the only cure I found now is my empty wallet and kid coming out of my wife's belly in a few month. I wanted to start and build guitars, but I am pretty sure if I start that, I am doomed! Same goes with amps. If I ever start doing stuff, my whole backyard will end up a guitar shop where I will spend even my food money in... So better just end up with the empty wallet and let the wife do the budget thing But yep, I gotta keep that GAS in check... spend at least 30k in gear the last 5 years... and lost A LOT with my gas problems. It was even pathologic last year (trust me, it can... same thing with lottery crap, but I am immuned to everything except guitars, bass and amps). Wifey want me to be a normal man and check regular porn instead of guitar porn (haha kidding... well, maybe I should ask...). Now, I just have the child getting the hang of my disease But hey, better late than never But I am cured now, understood a lot of things with time, first thing being : tone is in the fingertips. I can make a crappy guitar sound about the same as a 10k one, hence why I sold all my crazy expensive ones : I was just too stressed to gig with them, and ding and all. Guitar is beautiful, but you gotta take it easy or it can go hardcore on debts.

Happy to have gotten rid of GAS with G&L though. Now I mod my stuff, more fun and less costly Cheers!

[Elwood]

My AAS gets compounded with OAS (Organ Acquisition Sundrome) when
I see deals like this one. ($50!)




Craiglist link

If my van was running better...I'd probably ...dang, I gotta stop thinking about it

I've opened up that radio shack tube booster, pretty stout construction...all resistors are hollow core ceramic,etc.
...pics to come.

I found another NOS realistic booster...we'll see if daisy chaining 2 12au7 units makes for good sounds,
taming the gain structure is the fun part.
....and matching the input impedances, it works great after a buffered effect...not so much straight from the guitar.
I'll have to get some sounds up , 'cuz it does sound good

I wonder if my housemate would notice a second Hammond

[Elwood]

Interesting little bit of kismet...
I was rolling the pre tubes in my Swart SST, the reverb gain structure was(is) off,
so I went looking for a 12AU7 to bring things down a little.
I couldn't find a spare, then it occurred to me the Hammond has some
...a nice old RCA 12AU7 from the organ got me closer my goal.
I might put a little inline attenuator on the reverb circuit to get an even better balance of
dry and wet. I can't really change the reverb driver tube because its a 12DW7, the gain stages are
20/100, so I'm sorta stuck with that option.

The great news is the 12AU7 in V1 opened up the headroom on the reverb (as well as everything else)
and I'm loving the amp again, before that I have been considering letting it go.
I'm working on getting some vids going, I'll try to keep the noodling to a minimum

cheers

[Crusher]

Talking about tubes... I need to change my vox tubes, a little ac4c1 handwired. I need to change them, and found the tube store... but there is so many tubes brand, I don't know which one to choose!!!

Need 12AX7 (x2) + EL84 (x1)... suggestions? Tried to search what was in from factory, and wasn't able to find any clue!!!

[Elwood]

Need 12AX7 (x2) + EL84 (x1)... suggestions? Tried to search what was in from factory, and wasn't able to find any clue!!!

Here's a page that makes some quick comparisons of new tubes (by a guitar player even)
tubesandmore link

[geoff douglas]

Hi Elwood,
Did you fix the van and pick that Hammond up or was that another organ previously acquired for the valves,,
Just curious also if you re biased the 12au7. If the circuit is cathode biased and the plate and bias resistors calculated for a 12ax7 then due to the different plate resistance of a 12ax7 compared to a 12au7 ( which is huge ) , its most likely you will drive one half of your signal into clipping before the other as preamps tubes run class A. If you have a signal generator and a CRO it would be worth driving the front end with it and looking with the cro on the output on V1 to see what you actually end up with when varying the input level. Just a thought but typically i would not change such a huge amount. 12ax7 to 12at7, not so bad, 12ax7 to 12ay7, a bit iffy but 12ax7 to 12au7 is a step to far i would think..In a perfect world when changing any amp gain stages the resistors should be changed to ensure the tube is biased at 50% of the usable current range for that particular valve. This ensures an ability of that valve to swing up an equal amount to down enabling a true mirror image of the input signal though in an amplified state. This is worth keeping in mind especially if chasing clean tones.
Cheers Geoff

[Elwood]

That was from the working hammond, which I'll put back after the experiments.

No, I didn't re bias.
Thanks for the heads up, I'll bring the amp over to my tech so we can see what is going on.
I didn't realize the AU7's were biased that differently.
It sounds much better than it did, but that might be because one of the tubes I took out of
the mix was a JAN 5751. I hear they have a place in good tube amps, but this might have not been a good place
for it, or maybe the tube tests weak.
With the 12AU7, I gather the tone might be off, but I'm not in danger of burning anything up?

Before the changes, the reverb was being driven too much. The solution I'm looking for then might involve
a potentiometer in the reverb circuit to bring that signal down some. Then I can consider an 12AT7 in V1 if I want
to play with the gain structure.
Thanks for the good advice. I'll make a quick comparison video before I return the tube to the Hammond.
Hopefully my tech will be back in town soon so he can put it on the bench and I'll soon understand more.
I'm learning...slowly.
I don't really like playing darts in the dark.

thanks again

[geoff douglas]

Lol’ I was willing to bet you got the van going better, those meetings are working I see, loling still,,
About the Reverb gain level, there is likely another cause for that. Your tech could suggest some of the possibilities with you and if time permitted looking over his shoulder whilst hes investigating these possibilities is the ideal way to learn..
Regarding will using a 12au7 cause damage. It’s possible but unlikely. In cathode biased circuits there are only three things resisting a short circuit from the supply voltage and ground. They are 1/ the plate resistor between supply and valve anode/plate. 2/. The plate to cathode resistance of the valve and 3/ the cathode resistor to ground. This is in effect a 3 resistor voltage divider with the plate voltage and cathode voltage levels determined by these resistances in conjunction with how hard the valve is being driven by an input signal and the valves bias state. If you change any one of these resistors or the valve type the resultant voltages at the plate and cathode change accordingly. The issue arises with cathode biased circuits where the voltage at the cathode is feed to the Grid, the tap handle so to speak which controls the idling/biased condition of the valve. If a valve is biased hot, i.e. 70% of available current range is flowing through the valve at idle, then an input signal which increases current from the idle state can only rise 30% before the valve can supply no more current, at this point a flat line signal shape results, called a saturated condition/clipping. Negative going waves though can go low 70% of that available current before valve cut off occurs and signal shape flat lines. If a valve is cold biased though at say 30%, the opposite occurs. A positive wave can go 70% without saturation and negative waves only 30% low before cut off.. It is important to note that the output of a preamp valve at the anode is 180 degrees out of phase with the input signal because a more negative input signal actually turns a valve off more so plate voltage rises and a positive going signal turns the valve on more so plate voltage lowers. All to do with electrons which are negatively charged on the control grid repelling the supply of electrons from the power supply. Some amp designers like the tone of non- symmetric clipping and design their stages bias point accordingly, most distortion pedals use that principle too or a variation of non-symmetric clipping.
I hope this info wasn’t too boring but I get enthused and encouraged when others have a desire to learn, all knowledge is good knowledge I firmly believe. So glad your into it Elwood,
Cheers

[Elwood]

Lol’ I was willing to bet you got the van going better, those meetings are working I see, loling still,,

hehe...I've resisted looking at the link, hoping some organ enthusiast gives it a good home.
So, I might be making progress (ask me again after Sunday..LOL)

Your making sense, so I must be catching on...thank you and please keep it coming.
I'll read through it a few more times and use it a starting point for conversations with my amp guy,
he has been gracious enough to let me watch him work.
I'm trying to draw schematics of those radio shack boosters, that's helping too.
I'll show you my work once I think I'm close to being accurate.
...time to think about carpentry for the day, I have tomorrow off so I should be able to make some sample videos.
I think it's time I buy a Fluke, then a CRO.

Have a good day
Elwood

[geoff douglas]

Hi Elwood,, Its great that your tech allows you to trouble shoot with him, he sounds like a decent sort of guy.
I have edited my last post a little, its a bit difficult to explain this stuff in one paragraph so i do hope it is sort of understandable . May i suggest if buying a CRO for diagnostic use then a simple signal generator should be purchased as well. This will provide a sine wave of a frequency you choose with a variable level that you can feed the front end with instead of a guitar signal. That same waveform can then be monitored with the CRO at the different gain stages through to the power amp section. When increasing the input level you will also be able to see when a particular valve goes into saturation or cut off, the starting point of the overdrive tone we so desire. I look forward to discussing anything regarding amps with you and please never hesitate to ask any question you might have, if i know the answer im more than happy to explain the answer to you.
Cheers G

[Elwood]

I'm up late and playing with the Swart,

I'm remembering now why I have considered adding a trim pot to the reverb tank, and I think
it's due to the amp designers decision to have a split signal going to the reverb before the first
volume pot. (controls are Vol/Tone/Reverb/Trem dwell/Trem rate/Master Vol.)
The amount of gain I dial in on the first Volume has no (or very little) effect on the signal being
fed to the reverb. Turning up the Reverb gives a louder Reverb signal, but with no change in the sound
or length. I'm gathering the Reverb pot is after the tank in the circuit.
There are a couple sweet spots in combinations of settings, but I know(pretty sure) this amp can be more
than a one trick pony.
I'm going to put in a 12AX7 back in V1, (remember there was a suspect 5751 in there before).
So I'll run it through paces with a stock compliment of tubes, then I'll start again thinking about reversible mods.

I'll also fire up the little 18W Swart head and see if the Reverb response seems similar to the 35 watter. Maybe Micheal Swart and co. changed something between #10 and #18.

It'll be a good time to show you the undersides of them, they have real pretty harness work.
So more pics and stories to come, then some vids once I can settle into a groove.

Stay tuned

[Elwood]

Well, I had to make an amp cradle from the scrap bin,
not fancy and adjustable like the one I made for my tech...but it seems to work for now.
Here's some pics of the innards of the Swart SST30 while I consider my
mod options.







and a link to the Slickpic Album for bigger pics (plus a few).
Link

I think I see the first stage of the 12DW7 (reverb driver) being fed off a 6V6 pin, is that a common thing?
I've read the some Swart amps were inspired by the Gibson Scout amps...gonna have to keep an eye for those.
I have room for just one more amp.

cheers

[geoff douglas]

Wow, it does look neat doesn't it, very tidy indeed. Do you happen to have a circuit diagram for this amp Elwood, if you could post a link to one it would be good to see what is happening where in the circuit. I found a operators manual but no circuit diagrams. The reverb driver V3 appears to have a common supply with V1,2,and 4. Typically the preamp and reverb tubes are supplied at a lower voltage than the output stage. When you buy your fluke you need to consider its maximum voltage reading ability also, it needs to be able to read a minimum of 600vDC, the higher the better. Cheers Geoff

[Elwood]

per my memory...Michael Swart won't give up the schematics,
but he will happliy chat on the phone until a problem is resolved.

Thanks for the MM advice. My amp guy is willing to put on his bench
to see where it's clipping. I'll have more clarity on the circuit after that.
I'll report back pertinent findings.

One thing I found is I love a 95% wet signal with the tremelo on fast and full dwell,
it's very psychedelic.
Sound clips coming (soon, I swear).
Elwood

[brentrocks]

I'M GONNA JUMP IN ON THIS OLD AMP DISSCUSSION!

I ACQUIRED THIS 69 FENDER SUPER REVERB FROM A LOCAL FRIEND ABOUT 2 YEARS AGO. THE ORIGINAL 4X10 BAFFLE WAS REPLACED WITH A 2X12 BAFFLE. ALL THE GUTS ARE ORIGINAL. IT SOUNDS ABSOLOUTLY AMAZING!!!!

HE SOLD IT TO ME FOR $600

[geoff douglas]

What a great amp at a great price, that was your lucky day for sure,, I would be thinking of replacing the filter capacitors soon though, it only takes one to fail and it takes quite a bit more with it when it goes. Prevention is better than cure they say,,just a thought,, Cheers

[Elwood]

What a great amp at a great price,

+1
What speakers are installed?

With your silver sparkled ASAT, that's gotta be a winning pair...in both sound and looks

[Elwood]

When you buy your fluke you need to consider its maximum voltage reading ability also, it needs to be able to read a minimum of 600vDC, the higher the better. Cheers Geoff

Ordered a Fluke 179 today. I learned they started in Everett Wa. , a suburb of Seattle.
No discount for this homeboy (amazon had a good price just the same).

No turning back now...looking forward to my new tool .
Time to read the Tube Amp books cover to cover
I'll dig up another amp for pics when I need a break.

Elwood

[geoff douglas]

Nice choice the 179 Elwood, its always best not to half do something ,, So the world of live testing. 1st rule, no cats, dogs, any pets at all allowed when your live working. Understand please Elwood, slip with your meter probe, oops touch the wrong terminal,,,best not to think of the result of that. just be careful and precise on all testing points and all will be fine. rule 2,, dont forget rule one....

[Elwood]

I'll tell my cats that "I need a little me time".

Seriously, thanks for the good reinforcement of proper habits.

[FZTNT]

I dunno, I find cats quite useful for troubleshooting electrical circuits. When their eyes glow just right I know the circuit is sound and voltage is just right. If they do that arched back, fur on fire thing I have to get another cat.


JUST KIDDING. I don't want the ASPCA coming after me, just a little burnt cat humor. The kittens are also excellent for shark fishing. (oh no, not another one...sorry). No really, I love cats...

Tom

[geoff douglas]

lol,, your a funny fella Tom,,, That made me laugh

[Elwood]

What do you guys think this will go for?
$5,000? ... $10,000 ??


https://www.ebay.com/itm/Dumble-Special ... 3007670349

[DanDoulogos]

What do you guys think this will go for?
$5,000? ... $10,000 ??


https://www.ebay.com/itm/Dumble-Special ... 3007670349

At least 5K... That's an oldy... I wish there were some pics of the innards.

Did they come with that covering - I've only seen 'em in that sorta tan...(at that age)...? edit: Wait. that's a small special.... okay black makes sense now

[FZTNT]

What do you guys think this will go for?
$5,000? ... $10,000 ??


https://www.ebay.com/itm/Dumble-Special ... 3007670349

I'm not a huge amp aficionado so forgive the ignorance, but, what is this thing and why would it be worth so much especially since it does not work. According to the listing. I vaguely remember the name but that's about all.

Tom

[Kit]

Since this thread kind of meanders by itself I thought I'd steer a slight turn.

I also have a Swart AST and play it regularly with a band. Recently I realized that the reverb doesn't have the 'verb' that it did when I first got the amp, and that was about a dozen years ago. This morning I changed out the the old 12DW7 with a new JJ 12DW7 and got the reverb back to what I think I remember it was. I was under the impression that tubes don't degrade, they just burn out. But it is obvious that I'm wrong about that. I'm still not understanding how tubes degrade, other than the amp just doesn't sound like it use to, slowly over time.

This got me interested in doing a little experimentation with the preamp tubes. I've got Tung Sol 12AX7 tubes coming that I can try out in the preamp stage. And I'm looking at a better quality 12DW7 for the reverb circuit, perhaps an Electro Harmonix. I may be getting on the slippery slope here.

[Elwood]

As a Swart owner Ill be eager to hear your results.
Good news on the reverb,
I still haven't got mine dialed in...it's too hot and is distorting.
When my amp guy is on town, and he has time, I'll get him to put the scope at different stages
to hunt down the distortion.
I'm looking to get closer to that deep twin reverb sound d d d d . ..

[Kit]

Elwood, this is likely a most stupid question, but have you tried plugging into the 'lo' input instead? On mine I found plugging into the 'hi' input for some guitars lead to a lot more distortion than I want.

[Elwood]

Elwood, this is likely a most stupid question, but have you tried plugging into the 'lo' input instead? On mine I found plugging into the 'hi' input for some guitars lead to a lot more distortion than I want.

Yes, it helps some, but not enough.
...and even with a crystal clear sound, the reverb is woolly.
I'll be sure to post my findings.

Last I checked the Dumble was up to 1900 or so...
Tom, you gotta go down the Dumble rabbit hole that google will bring. Alexander Dumble is an icon worth knowing about. cheers

[Kit]

So I replaced the 12-year old pre amp JJ tube yesterday with a Tung Sol 12ax7. It is immediately noticeable that the amp sounded better. After playing it for a few minutes I suddenly had the thought "This sounds as good as how I remember it sounded when I first got this." Whether that is true or not I can't be definite, because the comparison is based on memory, but one thing I can be certain is that the amp sounds better now than it did a week ago. Mind you, the amp did not sound bad even last week; what got me onto experimenting with tubes was because the reverb sounded weak and I changed out the 12DW7 tube that drove the reverb circuit. And that took me down the path of replacing other pre amp tubes to see what happens. At this point I have the Tung Sol in V1, a new JJ 12DW7 n V2, and a new JJ 12AX7 in V3. I am waiting for an Electro Harmonix 12DW7 to arrive in the mail.

Here's what I hear different from the amp now compared to last week. There is less of a hum when I take the amp out of Standby (at band practice I never even notice the hum, only when I'm at home in a quiet room am I even aware of it normally.) Notes played sound cleaner than before. Bass and mid-range sound about the same as before, the amp now has a bit more treble than with the old tube. Both the effects: reverb and tremolo, sound better too with the Tung Sol.

I don't know enough to spring for NOS tubes in my tests. The JJ tubes I got locally from Eurotubes because it is located in Portland where I live. The Tung Sol are current stock made in Russia, and that is also the case with the Electro Harmonix on its way. The Tung Sol 12AX7s cost only a few dollars more per than the JJ, and so far it seems well worth it.

Since I have another Tung Sol 12AX7 I may pop that in V3 and see what difference that makes to the tremolo. And when I get the EH I'll test it in V2 for reverb.

One last thing I should point out is that I got my Swart AST used. It was about a year or 2 old when I bought it 12 years ago. Within days of getting it the rectifier tube went out. And in the process of diagnosing and fixing that I ended up with a complete set of JJ tubes for the amp. And that's what has been in the amp until last week.

[Elwood]

Yesterday I finally got my Swart SST30 over to my amp tech (Bruce) to chase down the distortion
in the reverb circuit.
We checked the tubes, they checked good. Swapped out some other reverb tanks...not it.
Bruce re-tensioned the 12DW7 socket (reverb) and we both could hear a slight improvement.
We let it rest for the night.

I came back this morning with another 12DW7 to swap in case it was a bad tube.
Bruce had a hunch, so before we dived in deeper...he re-tensioned all the pre tube sockets.

That was it !!
Loose connections were the cause of my reverb sounding like an amp in a large coffee can.

Cheers all.
May your pins be tight and your tubes glow nice

[Kit]

Yesterday I finally got my Swart SST30 over to my amp tech (Bruce) to chase down the distortion in the reverb circuit.

I came back this morning with another 12DW7 to swap in case it was a bad tube.
Bruce had a hunch, so before we dived in deeper...he re-tensioned all the pre tube sockets.

That was it !!
Loose connections were the cause of my reverb sounding like an amp in a large coffee can.

Great news! Sometimes it works out that the simple problem is the culprit, but finding it is always frustrating.

I was playing around with preamp tubes on my Swart AST a few months ago and one tube that I tried had skinny pins and sat really loose in the socket. I read up on it a bit and tried bending the pins to angle them to make the tube sit tighter. Not having much experience with tubes I was nervous doing it. I made it work OK, but eventually settled on a different tube in that position.

Still happy with my amp after more than 10 years.