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Messages - tonyharker

#106
Amplifier Discussion / Re: debugging a small amp
May 11, 2011, 11:39:34 AM
Sounds like the preamp is at fault.  Did you build it yourself from a kit or was it ready made?  Do you have the circuit for it? 
#107
Usually when the output transistors fail, the drivers and sometimes the VAS transistors go as well.  I suggest you check those as well otherwise you will need some more 2N3055s. :)

Tony
#108
Not a Tiger then as I think all they were all Fully Complementary.  Probably a generic RCA design, 70 watts for sure.
#109
Difficult to tell from the small pictures, but from the appearance of those transistors with square heatsinks, it looks to be a variation of a Tiger amplifier from Popular Electronics magazine. Are these transistors RCA types with the numbers 40409 & 40410?
If the outputs are TO3 types 2N4909, & 2N4915 then the amp is likely 100w/channel.
#110
There are a number of car radio ICs which would do what you are asking.  TDA 2003 for example. You may need to use two 4 ohm speakers to get the output you want or use two in a bridge arrangement for a single speaker.  Check out the TDA 2005, this has two amps in one chip and can be bridged for higher power.
#111
Pin 5 is connected to ground via switches on both input jacks to reduce noise.  When a plug is inserted into a jack this connection is broken.
#112
Hi Steve I've now got your schematic, must have been a glitch with my Acrobat reader, as it was showing just a black screen.  Im a bit puzzled, your circuit shows the boost transistors in emitter follower mode fed from the output transformer.  How then can you get 30 watts out of them if there is no gain in the circuit?   EF circuits have a gain of less than one and you are still using an 8 ohm speaker.  You would need to amplify the output from the transformer (ie 3w in 8 ohms is about 5vrms to 30w in 8 ohms is 15.5v approx) by about 3x ???
#113
Your link to the schematic is not working, can you fix it please as Id like to try this on one of my amps.
Thanks  Tony.
#114
Tubes and Hybrids / Re: How Hard Would It Be?
August 15, 2010, 02:00:47 PM
There's always this < http://cgi.ebay.co.uk/New-product-MKII-12AU7-buffer-amp-Tube-/260644578435?pt=Vintage_Electronics_R2  >  this shouldnt be too difficult to adapt.  This runs off 12v boosted on the PCB to about 45-55v to power the tube.
#116
As I understand it the ECC83 is the same as the 12AX7.  The EC83 if it follows European nomenclature should be only a single triode not a double like the 12AX7.  The E stands for the heater voltage (6.3v) and the C for the type of tube ie triode.  if it was an F it would be a Pentode as in EF84.

Similarly for the EC82.

Tont
#117
These usually slide off sideways :)
#118
I would just change the transformer for a 120v version and the mains plug for the correct type. You can use the same cable.
I would also increase the fuse to 2 amp rating. 
Stick a label over the Input Power rating with the new details on it.
#119
Amplifier Discussion / Re: Mod an OLD amp?
April 20, 2010, 10:47:20 AM
Didnt you like the answers you got on the other forums? Or are you waiting for someone to say yes you can do it like this :)

I'm afraid you are asking too much from an old amp like that, you cant do what you want without a major rebuild.
#120
What power supply are you using?  Motor-boating is usually caused by the supply not having enough capacitance across the + & - rails i.e. too high an impedance.  You should have at least 2200uF but more is better. 
Another cause is the supply not being able to supply the current needed by the amplifier.  20 watts peak into an 8 ohm speaker would need approx 1.5 amps. 
This cannot be supplied by the same battery as you used for your little Gem!

Tony.