Quote from: E on April 02, 2010, 08:29:41 AM
i made a copy of the PDF without the giant 'www.epmag.com' in the middle of every page so you can actually see the diagrams.

So How did you do that then? Huh!!

Tony.

What about this one < http://www.national.com/mpf/LM/LM380.html#Overview > ?

Tony.

LM386 isnt really an Op amp but a small power amp.  It has an internal reference to earth of 50K.

Edward, just a little criticism - would you please not post in capital letters
1. It is difficult to read and
2. It as seen as shouting which is rude.

Regards  Tony.

Why not try a noisy cricket?  There should be enough info here < http://www.beavisaudio.com/projects/NoisyCricket/#Intro >  to tell you what to do.

Are you mounting the speakers on the front of the baffle or on the rear.
I normally mount them on the rear so that the speaker cloth/grille fits flush with the front face of the baffle board. 
Alternatively you can rebate around the speaker hole, so that the speaker is inset.

Regards  Tony.

Well the AER Compact 60 runs from the AC mains either 110v or 220/240v. The official consumption is about 70VA.
To run that from a 12v battery you are going to need an inverter.
I don't know where you live but something like this < http://cgi.ebay.co.uk/Top-150W-Car-Charger-Power-Adapter-Inverter-12V-TO-220V_W0QQitemZ280456875174QQcmdZViewItemQQptZUK_Home_Garden_PowerTools_SM?hash=item414c884ca6 > with a car battery and a battery charger.  The battery will have to supply the 70VA - probably more like 100VA because of all the losses in the inverter say some 8 - 9 amps.
A 40AH car battery should last you approx 4 -5 hours before needing a recharge.

You should be able to build a cabinet for the battery, inverter and charger to match the amplifier but it will be mighty heavy.

Alternatively you could drive the amplifier directly from internal batteries but you will need a schematic to find out the internal supply rails. These will probably total about 65 - 70volts.

regards  Tony.   

Just looked at the characteristics for the Philips EL84.  For class AB Push pull grid bias should be -14.7 with B+ at 300v and -11.6 with B+ at 250v. 
-30v is sending your EL84s into cutoff which is why you are getting so much distortion.  The quiescent plate current with no signal should be 7.5mA in each tube.   For 17W output the plate current should be 46mA.  so your original bias of -14 was correct and you should get your tech guy to put it back to that value!  Alternatively get someone else to look at it who knows what they are doing! 
Regards Tony

You definitely have something wrong.  Varying the volume should not change the output DC voltage. 
The voltage at pin 5 should be about half of the supply voltage (eg 4.5 volts if you are running it from a 9V battery). 
Are you building it on the Radio Shack board?  Have you tried swapping the IC as you may have a dud one - it does happen.  You did use a socket didn't you??   I dont know what else to suggest.

Have you thought of using an electret mike element as a contact mike?  These usually have a FET preamp built in all you need to do is supply it with volts from a battery.  They also usually have a high output level.

Tony.

What you appear to have got is a dirty input jack.  The crud on the contacts is acting as a diode detector for radio signals.  try replacing it with a new one preferably with gold plated contacts.  Also a small value capacitor about 10 -15pf across the input of the amplifier will also prevent the amplifier detecting these signals.

Please write in English - we would all like to understand what you say!

Yes definitely 220 Volts!  Dont know what transformer will be fitted inside but this < http://cgi.ebay.com/100-Watts-Step-Up-Down-110-220-Volt-Transformer-Adapter_W0QQitemZ120408405373QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1c08e6757d > would be easier than replacing it and probably cheaper too.

Tony

Is is this one?  < http://cgi.ebay.it/AMPLIFICATORE-PER-CHITARRA-ELETTRICA-CASTLEY-30W-GA30_W0QQitemZ140354506538QQcmdZViewItemQQptZAmplificatori_per_Chitarra?hash=item20adc7cf2a >  If so it should say on the back what voltage its for but if it has a European plug then it would be for 220-240V.  To use it in the US on 110V you would need a step up transformer or change the main power transformer.  

The seller on ebay appears to be Italian - also beware!  it says on the back that the chassis is HOT?
This could mean that it has a high temperature in use or it could mean that it is LIVE

Regards  Tony.

From what you are saying it sounds to me that the chip is oscillating.  You may have the input and output leads or circuitry too close together especially if you are using matrix board.  The 6800pf going to ground on the TV amps may have been put there to stop this.
By the way Pins 2 & 5 are ground.  Ignore the + in the symbols munkey used he has probably just cut and pasted the same ones.

Tony