Tweakers' Asylum

RE: Heathkit IG-18 mods 2008?

71.198.200.53

ironbut

In Reply to: RE: Heathkit IG-18 mods 2008? posted by PhilH on December 21, 2008 at 12:57:01

Thanks Phil, here's the info related to the 40408;
The added circuit is a simple emitter follower.The transistor I used isn't too critical, so long as it has a Vceo greater than 45.
Regarding the 2n5687;
I increased the current gain of Q3 by converting it into a compound pair/adding another transistor.It should be a high hfe, low noise device with a Vceo of not less than 45V and must be a pnp.

Follow Ups:

RE: Heathkit IG-18 mods 2008? - PhilH 13:50:59 12/21/08 (3)
For the potentiometer, check Mouser stock # 31VW601 at Mouser.com

Mouser sells Zetex transistors that might work OK. Look at ZTX651 (npn) and ZTX751 (pnp). They also have a PNP Darlington if you need even more gain -- ZTX705

Hope this helps. I have a IG-5218 with the Walter Morrey "Super Oscillator" mods from Audio Amateur (Issue 4/75) but I think mine needs a little work too.......

Phil
- another thought - PhilH 14:04:39 12/21/08 (2)
  I once also considered just gutting IG-5218 (keeping freq & amplitude switching capabilities) and using the "Ultra-Low THD Oscillator" circuit from the data sheet for the LT1115.
  - RE: another thought - ironbut 15:17:35 12/21/08 (1)
    Wow, thanks a million Phil. I'll have to check these other options out. I've got a little time on my hands so this is a good time to do this kinda stuff.
    - RE: another thought - PhilH 14:04:44 12/22/08 (0)
      You're welcome and good luck. I'd be interested in learning what you end up doing so if you have some successes, please post them if you can.
      
      thanks
      
      Phil

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