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Messages - nodz

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Schematics and Layouts / Re: Valve Tremolo - Help Wanted Please
« on: December 28, 2020, 08:30:26 PM »
Rightho, finally found the original doco.  Phase shift oscillator where O/P is capacitively coupled to the plate of the first stage audio amplifier.  I coupled it to the intermediate mid drive amp rather than the first stage.

Schematics and Layouts / Re: Valve Tremolo - Help Wanted Please
« on: December 26, 2020, 05:00:20 PM »
That is why your circuit will not work.  Trem will only work if it is introduced into grid or cathode circuits.

With respect to my amp
So if I took the O/P from the trem unit (section A) after the 0.056uF coupling cap and introduced it at the junction 0.022uF (C14)  and 1M (R16) of the grid of the PI (Section D) - all well and good?

So basically free running LFO mixed with the signal from Sections A & B, without having to actually have seperate trem channels as per

Schematics and Layouts / Re: Valve Tremolo - Help Wanted Please
« on: December 25, 2020, 01:49:00 PM »
Understood that it normally feeds the bias of say the phase inverter of output.  Perhaps I should have included the full circuit, in that the tremelo is connected to the plate of the next stage 1/2 12AX7 which in turn connects to to the 12AX7 phase inverter.  So very similar to say the Fender concert schematic attached, I've labelled the 'similar' sections of the two diagrams for comparison.  The tremelo on the Fender concert uses 4 x 1/2 7025 but the O/P is connected to plate of Section C, which both in turn connect to grid and bias of Section D the PI.
Section A tremelo unit
Section B tone stack
Section C Intermediate amp (I've used it as a mid drive/master volume section on my amp)
Section D PI
Section E PA

Schematics and Layouts / Valve Tremolo - Help Wanted Please
« on: December 24, 2020, 03:30:47 PM »
Hi All,
Was wondering if anyboy could help - attached is a schematic that was drawn up by me to add a valve tremolo to an amp.  I obviously used certain reference data, schematics etc but for the life of me, I cannot find the original schematic and what I have drawn up doesn't appear quite right.  The only diagram I've managed to find is that of the Symphonic MA50 amp (?) att.
My original schematic uses 6AT6 as trem with F/S, Speed intensity controls driving a second section that was between the tone stack of the first stage and the phase inverter.  What is strange is that the O/P of the trem unit is fed to plate of second stage and not the grid.
So question, is the schematic correct? WIll it work? What have I messed up etc.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: July 05, 2013, 08:46:03 AM »
That's good if they have their own fuses. Makes the wiring up much easier.  Just an on off switch and the standby switch to worry about.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: July 05, 2013, 04:13:45 AM »
Hahaha yes Phil.  What I meant was, is all I need a fuse of a small value on the ht side of the transformer because I am using an a.c. wall wart multiplied up

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: July 04, 2013, 11:12:09 PM »
Just wondered now, that I have built the PSU by taking the AC output from a wall wart and then multiplied it back to 240V from a back-to-back transformer, whether I need some kind of over-current failsafe to prevent damage to the Wall wart, PSU and preamp.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 16, 2013, 06:52:01 PM »
Quote from: Roly
I rat caps out of CRT TV's at the local dump...

I get them from CRT too.  Whenever a mate gets rid of one, I get them to drop it over to my place.  I then take various bits and pieces out of them and then dump the rest.

I will be doing that with the old computer PSUs now, so that I can gather together enough hi-voltage caps for voltage multipliers.

Quote from: Roly
"Where do you keep your transformers?"
Blank look from young sales dweeb.
"We don't stock toys" he sneered.

Oh you had this problem too. :lmao:  Towards the end of the component stocking days, I'd walk in there and they wouldn't have a clue.  I wanted an electrolytic cap of a specific value, bloke looked on the computer and said they had stock and then tried to sell me a ceramic cap for $20.  What I wanted was a hi capacity one for use in a 13.8V, 10A PSU for amateur radio supply.

Hopefully, I won't need too many bits to get moving on the preamp.  I'll be reviewing over the next couple of days

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 15, 2013, 03:32:05 PM »
Quote from: Roly
A lot of builders make the mistake of miniaturising their board build, then putting it into a large case   - just making life difficult for themselves.

Since I am building modular and probably going to build into 19" racks for ease of use and storage around the home, size is not really an issue, except height that is.

The 2 x 100uF/400V caps that are in the HT supply line, were snap-ins.  I just straightened the pins slightly with a pair of needle nose pliers and soldered them to the board.  I'm a fan because of their half height, although they have a larger footprint.  For some reason this type of capacitor is cheaper new than many of the others.  I bought a packet of 6 for $9.  It means that they fit in a 1U rack easily.  If i need to buy, rather than scavenge, I buy at and they quite often have specials like that.

Years ago when i was regularly building amateur radio projects and when Dick Smith's was not just a home entertainment store, i used to buy in bulk.  I have 200 x 1N4004 diodes, that I think were $5 for the bag, so as I said for the sake of a 2 cent diode to protect a $2 regulator, cheap insurance.

Over the next few days, will be sorting through the junk box to determine what is needed for the preamp.  I think that I have most of the components, just a few pots and resistors needed, I think.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 14, 2013, 06:06:16 PM »
Woot, woot.  Preamp PSU completed.  R2 - 2 x 1K2 in series, R1 - 270R for a calculated 12.36V.  Actual measured voltage 12.5V with no load.
Changed out regulator, just in case.
Replaced the second 4,700/50V cap with a 100uF/25V, no problems  :tu:
Placed a diode across I/P & O/P, may not be required now that large cap has been replaced but for the sake of a 2 cent diode.
Simplified circuit diagram attached.

Board is larger than probably necessary, but I deliberately spaced everything out for ease of trouble shooting and repair, should it ever be required.

Tested supply on heaters of an ECC83 valve.  Nice glow.  :cheesy:

Thanks for the input, definitely some head scratching there for a while.

Now to start rounding up all the parts for the preamp.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 11, 2013, 03:26:47 PM »
Rightho changing heaters to 12.6v. I did have a diode across the lm317t but I thought that this may have been the cause of the problem so I removed it.  Will change the capacitance to something like 10uF, will see what I have.  Will remove the elevation link then when put the circuit board into the case ensure that both circuits are earthed properly.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 11, 2013, 08:46:58 AM »
Most of the ideas are taken from audiophile circuits.  Pretty much a standard circuit for hi-fi preamp.  Perhaps may be overkill for a guitar amp but was potentially going to use the PSU for a hi-fi preamp as well.  Might try losing the voltage elevation link for the moment and just working on the heater by itself. I can change out the 270 resistor and replace with a 220 and I can just have 2 x 1k resistors in series for R2, voila 12.61volts.   I''ll see what else I have in my junk box by way of a smaller cap with approx 25wv to replace the 4700uF.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 10, 2013, 08:19:20 PM »
Will have to check over, especially around that area
PSU is on veroboard.
Attached diagram shows how it is wired
Anything obvious from that?

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 09, 2013, 11:45:55 PM »
Appears to be a problem with R2 supposed to be 1K and 100R in series.
When I measure R2a its 100R, when I measure R2b it's also 100R even though it's marked 1K.  When I measure the resistance across both R2a and R2b expecting 1K1 I get 0 ohms.  Something very fishy.

The Newcomer's Forum / Re: Newcomer, Melbourne, Australia
« on: June 09, 2013, 09:03:49 PM »
RIghtho, Just wired up the PSU for the preamp as shown in the diagram.  All voltages as measured as shown also.
All seems to check out except for the heaters.  I was expecting a calculated 6.34V from the LM317T as per spec sheet, that is,  1.25 x (R2/R1 + 1).
R2 is 1100 ohms (a 1K and 100R in series), R1 = 270 ohms.
No matter what I do, all I get is 1.247V, which to me, doesn't seem correct, effectively R2/R1 appears to be 0???

Pin 1 is the adjust
Pin 2 is the output
Pin 3 is the input

My understanding this was from left to right when the device was viewed from the front, i.e the plastic part closest to you and the metal tab at the back furthest away from you.

Can anyone offer any help please??


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