Quote from: g1 on January 14, 2025, 01:41:37 PMYes, maybe it would be better if it was called the 'break-time' switch. 

I understand what Merlin says about cathode stripping being a myth, but I prefer to use the switches as prescribed by the manufacturer for turn-on and turn-off.
He gets very adamant about his anti-standby stance and it ends up putting me in the "methinks he doth protest too much" zone.

I have suspicions about tube warm up possibly being involved with tubes going microphonic, but have absolutely no hard data to back that up.

Well for me personally I'll only live for another 20 or so years so whether I use the standby or not the Valves will still out last me.

It's interesting to note that nearly All those old mantle radios and Gramophones did not have a standby.

I once inquired about an old Mantle Valve radio in an Antique shop which had been owned by the same Family for 3 generations.
The owner who would have been in his 60's told me that it belonged to his grandad. It had been running every working day since he could remember.

I think this falls under one those unsolvable mystery options like;
Some people leave the toilet seat down while some people get nasty if you leave it up.  
My wife lost here wedding ring down the loo because she used to leave it up.
and I said,, "well that is why they come with a lid dear"  

YMMV, cheers, Phil.

If you think about it there is a clue in the word ""Standby"".
Band takes a short break, flick it on standby so when you come back flick the standby and play. There is no waiting for the amp to warm up again.

To me that would have been the obvious logical reason for the Standby switch.
No doubt there will be some monster circuits that need warmup time before HT is applied but for most small to medium wattage amps don't loose sleep if you forget to switch to standby before you power up.

I recall reading long ago that there are some standby designs that cause more harm than good.
Phil.

Quote from: ancient_places on January 07, 2025, 03:34:59 PMI've just recieved the amp in the mail and got a little time to play through it. It's in good shape and works, but there's a constant underlying hum that makes me feel like a recap is the wise way to go forward. 

Replacing caps in blind faith assuming that will fix it is mugs game,, Far more likely you have grounding issues.
Ground plane isssues can be hard to track down.
Schematics don't tend to show where they all connect, you just get a whole lot of Arrows pointing to some elusive Ground/Common path.
Finding that path in the actual Chassis can be confusing.
Some sockets use the metal outer ring to ground to the chassis but over time corrosion can cause the grounding path to fail causing hum.

Every Amp builder uses a different layout so you have to work out where each ground node interconnects back to Chassis common.


If it has a reverb tank that can be a hum issue
Phil.

Quote from: joecool85 on December 19, 2024, 11:18:18 AM

Quote from: phatt on December 18, 2024, 08:08:54 PMI personally like to put the Fuse First but up to you.
Phil.

100%  Always put the fuse as the first thing inline with the power input.  That way if there is an issue with the switch, or anything after the switch, the fuse will take the heat.

You got it, also I'd add that keep Main wires Separate from Secondary wires for extra safety. I've seen a lot of Big name brands tie Primary & Secondary in a bundle and it's not allowed in Military and Medical electronic Equipment for the obvious reason that if there is a Catastrophic failure it could connect mains to YOU which obviously would not go down well in a hospital.    

For clarity, Here is what the Poly Switch replaces in a power amp circuit.
If your amp already has the Current limit setup you can still Add the Poly Sw for extra protection. BTW The extra bonus is also protects your speakers. win win  
Phil.You cannot view this attachment.

My thoughts and experience on this issue FWIW,
You can save a whole lot of drama just by inserting a Poly switch on the output terminal of any power amp that does not have protection.
Simply by using a Poly Switch which is a resetable Solid State Fuse called a
"polymeric positive temperature coefficient device" (PPTC) Some times called polymeric PTC device or simply called Poly Switch.

These things are cheap ($2~3) and having used these on a few Amp builds I can say they work as intended.
They come on different sizes so you just need to know the full power current of your Amp circuit to match up the right one to use.
Here's a link to Altronics page I purchased mine from in Aust.
https://www.altronics.com.au/hardware/fuses/?type_1=ptc-polyswitch&srsltid=AfmBOopVtjMMNff1hDVmDTor3xGW21LYeTkEGn2Q1QzeRm4Zsm11_Hzv

I'm surprised they are not more widely used as they are perfect for the job especially as they save all the fiddly extra components needed to implement the current limiting which is often more than 6 extra resistors, a couple of diodes and 2 transistors which takes up extra PCB real estate.

I've forgotten the specs but obviously they switch lightning fast. Because I've tested my 80Watt DIY build and while at full power I Dead shorted the output over and over and that Amp was built 10 years ago and still runs fine today.

The yellow case does actually darken to orange as they get close to the limit. You can hear the Sound start to fade just before they trigger. Once triggered and Short removed they return to normal in a matter of a few seconds.

In my view ,, Perfect for DIY home build Amps.
Phil.

Quote from: saturated on December 22, 2024, 03:03:15 PMI am seeing old Dukane 🎤🎙� mic preamps and they have stuff like "24v DC input"

Wondering if there is/was a specific reason for this 

Maybe the answer is because it works? Idk 

Btw HAPPY HOLIDAYS 🎄 🎁

Main reason, it keeps the mains hum (EMF) from iron transformers out of the chassis which keeps hum interference as low as possible. A lot of pro mixing desks have outboard supply.
Phil. (Happy Crissy to all)

Yes that will work.
Just note that C5 & C6 should be no more than about 10uF as the regulators have already done the hard lifting.
I can't recall but big caps there can cause issues.

Not critical but the diodes only need to be 1N4004, 1N4007's are rated at 1,000volts. while 1N4004 is 400Volt, plenty of head room and slightly less voltage drop.

I personally like to put the Fuse First but up to you.
Phil.

99% chance You just blew your output transistors.
Buy new ones, and this time make damn sure with a meter continuity test that there is no short between the transistor and the heat sink **Before you power on**. you might have also stressed other components by doing this, So be warned you will need to use a **limiter** when you replace the power transistors as the other driver transistors might have failed as well.
How to make a Lightbulb limiter; https://www.ssguitar.com/index.php?topic=2093.0

As has been explained already,,,
You will not without major alteration be able to eliminate the pop.
Sorry if it sounds harsh but you just created a much bigger problem for no good reason.
A wise man once said;
"If it ain't broke don't try and fix it" 

Thanks Jay (I assume) I appreciate the effort you have gone to, to explain it all.
I know it must be very frustrating for you.

I had a hair line crack hidden under a solder pad in an amp that drove me nuts for a very long time. It was by chance that I turned the amp on just before I turned on the bench light one evening and saw a tiny flash on the circuit board which led me to the answer to the intermittent bad hum.
The crack was one of the main filter caps solder joints. The slightly over filled solder was covering the Crack in the copper track.
Phil.

At RG100
From post11,
When you say;
  "It used to sound just like the tone in the Dokken 'Just Got Lucky' (guitar only) video."

Well there are a lot of things besides the amplifier that can alter the outcome.
so,,, the Q you need to ask yourself is,
What was your whole setup before it all went south?

Did you change speakers? Did you change PU's or electronics in guitar?
Many things besides an amplifier can easy rob you of sound quality.
Just changing speakers can alter tone in a DRAMATIC way. 4 G12's in a box will sound very different to a single G12 in an open back cab
Some speakers might flab more so that others.

At post 13;
You mentioned you have taken a speaker out of the Randell cab and mixed in another speaker. That will change the sound big time when compared to the original Quad setup.
How about going back to the setup you had BEFORE it went wrong,,,then start all over again.

Dirty or corroded connections can cause signal loss, guitar cords can slowly cause signal loss due to broken strands. It seems to me that you have made a false assumption,, ""as G1 has noted there is no crossover distortion.""
And besides biasing ANY amp hotter does not make for better tone.
A Bias pot is NOT a Friggin GAIN knob. It has nothing to do with the gain of the amp, it just sets the balance between the 2 output devices.

Yes there is a lot of hype regards to biasing Valve rigs hotter to get the Mojo sound. well they don't understand what they are talking about. I have shown a few players in real time the sonic result of hot verses cold bias.
Here is what happens, with hot bias the amp starts to break up on 4.
With cold bias it starts breakup on 7.
So hot or cold the amp sounds the same. only Q left to ask the owner is how often do you want to replace your power valves.

The SS amp design you have is not going to give you power amp Dirt or sag as they don't work the same way. Valve amps have a soft power supply while SS use a stiff rigid PSU but you can design them to sag a bit with some mods.

If the Amp is working,,,My advice, go back and Establish just where it all went wrong. Because it's a fair bet something else might be the culprit.
Phil.

Hi daydream,
Ok, look at the right hand side of Schematic, note how you have 5 sockets.
These are switching sockets, meaning when you insert a plug it also switches the signal path.
Know this; FX loops and like are a nightmare, just waiting to go intermittent.
I personally hate them       

Spray the hole with De-oxit then plug a lead in and out 10 times. If that does not help then the switching tabs inside might be dead.
Now rather than trying to replace them it's far simpler and cost effective to simply take a short lead and bridge the send/return which bypasses the switch.

I have done this simple fix many times with failing FX lopp setups.

If it's the internal switching in the head phone, well that is harder to fix.
You would need to work out a bypass or replace the socket.
Hope it helps.
Phil.

You need to get priorities in perspective.
forget the preamp the power amp has blown so please focus on that first. Fix one issue at a time otherwise you just make life hard for you as well as those here trying to help you.

If it's all too hard to follow instructions then it's a fair bet one or more Tr's have blown so you could just replace them from Q10 onwards, with equivalent or higher rated. Q8 & Q9 are likely ok as they don't have to pass big current.

Then with no load and light bulb limiter bring up the voltage and check DC voltages shown on schematic. The bases of Q8 & Q9 as well as the speaker out should be very close to zero volts. (i.e. under 100mVDC)

****Be aware this circuit has No Short Circuit Protection like later designs so even a momentary short at speaker out will likely blow transistors****
 No need to ask me how I found that out 
This is a very simple circuit so a good learning curve for you.

The simple fact that the trace burnt out tells you there has been a critical short causing big current to flow and melt the copper trace.
Take it one step at a time.
Hint listen to G1,, He has the experience to help you.
Phil.

Quote from: RG100ESROX on October 28, 2024, 10:17:41 PMWell, no sound. Other than the somewhat  diminished hum/buzz that I had previously.

I tested the thermistor and it worked very well when heat was applied. So, I don't think this is my issue.

I changed both TIP32C's and the one TIP31C. And both 1N5484's located near the bias trim pot.

Any thoughts??

What should I be checking next??

1N5484 is suspect,, No such diode can be found in my quick search.
The Schematic says 1n914 which are just small signal diodes.
Using the wrong part at that point will likely end in smoke.
don't frig anymore until you build the light bulb limiter.

This is a DC Amp which means, All the Tr's sit at different DC potentials so if something fails it can take out many parts in a flash of magic smoke.
Now I'm not the expert here but here is a brief run down.

Unlike a Valve amp there are no coupling caps between active Tr's, hence the term DC coupled (no Cap to decouple the DC of each section) The limiter will save $$ and lots of wasted time.

The input is similar to the PI input to Valve power amp, used differently.
The idea is to keep the bases of Q8 & Q9 And the Spk output at close to Zero Volts as possible. Q10 is the Voltage Amp. (I think these Tr's see the biggest voltage and I think they tend to run hotter than output at times)
Q11 & Q12 are predrivers for the Darlington pair outputs, formed by Q13 & Q15 and Q14 & Q16. The diode string and trim pot from Q10 is the bias circuit. the thermister usually mounted to heat sink tracks the heat and slightly alters the bias as the amp heats up.
Google differential SState power amp designs or something like that .. Phil.

Ed I just found this; https://www.eeeguide.com/bjt-power-amplifier-with-differential-input-stages/

You just need a 100k pot in front of "C", the input to the Power stage.
If you can only get to halfway before it distorts use a 50k pot or add some series resistance before the 100k pot. Your ears will tell you if it way off.
Phil.