Germanium Amplifier

For the three and more legged things
Post Reply
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#61

Post by Mike H »

Me germaniums have arrived! Image



The complete collection:

Image



Image


Image


Even get a mica insulator kit in the box.


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#62

Post by pre65 »

And we want to know what it sounds like by the end of this week. :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#63

Post by Mike H »

Image

As likely as ... something quite unlikely

It'll sound ecstatic no worries

Need to think about some sort of chassis gubbins to put it on, and need to sort out heatsink fixing, brackets and wotnot. And boards. Also need a power supply.

 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#64

Post by Mike H »

Have just obtained a stock of the old style mylar caps so that takes care of the tone controls and wotnot caps re what to use.


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#65

Post by Mike H »

While I was still in the mood for messing about with boards I thought I'd run this up.

The power germs ensconsed into their final resting places

It's a bit bigger than I thought it was going to be!



Image


Image


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#66

Post by Mike H »

Earlier today spent about another £60 on Panasonic elecs and CC resistors for this, it's getting pricey for something that was originally just going to be a box of bits back-burner project to fiddle about with when I can't find anything better to do Image

It better work after all this, is all!


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#67

Post by pre65 »

Always amazes me, when you try something "cheap" using bits laying around and find a "few" bits and bobs to finish it off come to £50 or so. :(
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#68

Post by Mike H »

Isn't that always the way! I guess because usually when it comes to the point you don't actually have everything

Doesn't help if you keep changing your mind about what to use


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#69

Post by Mike H »

A quick fit-up of parts to see how things lie


Actually wasn't that quick, did take a wee while!


Image


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#70

Post by Mike H »

Problee shouldn't keep calling it "Transis-Tronics" anything because the designs are deviating more than somewhat from the original...


Anyway, not did anything further than the above, cos I wasn't entirely happy with the biasing arangement, including the temperature compensation.

What I really want, is something more cleverer like say one half behaves like a CCS for DC biased conditions, then the other half can be just trimmed to match until the o/p point is at Vcc/2 :?:

That's the theory anyway ~

This kind of thing ~
Part in pink, acts in the CCS role by virtue of being biased by J1. Another advantage is J1 will reduce its current with rise in temperature so help to stabilise the quiescent current due to temperature changes. In addition to the 1N4148 diodes (hitherto would have been OC91, except the V-drop is very variable depending on current, silicons are much more likely to stay in the 0.5 - 0.7 range.

Anyway in theory set up J1 for 48mA say. In other words drop the 330R resistor R15 twixt Vcc and 'P', adjust J1 (R8 will be variable) for 16V at 'P'.

Part in green ~ disconnect R15, 'P' goes to bottom, adjust R7 (variable) until 'P' comes back up to 16V.

Whether it will stay there is another matter. :D


It keeps 'P' in the middle because of R6. If 'P' goes down the Voltage across R6 increases, so does the current, from which the bias is derived so the green half pulls 'P' up. If 'P' goes up the Voltage goes down, etc. etc. so the green half current falls and the pink half pulls 'P' down. I did try it with two current sources like J1, one in each half, but it would either go straight to Vcc or 0V and stay there.
Attachments
Transis-Tronics Pwr-amp-10.gif
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#71

Post by Mike H »

"Accidents" ~

If R8 (preset) goes open circuit pink current falls to zero (or very low), 'P' just goes to Vcc; if R7 (preset) goes open circuit green goes to Vcc (same as previous), but pink keeps passing its basic set quiescent current.



 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#72

Post by Mike H »

I came across an unexpected problem, all this time (or mostly) I have been simulating it with a 8R load attached.

Took it off to simulate setting up the output bias current (a procedure that begins with wanging a 330R resistor beteen supply and output) and found A. it's very unstable with no load; B. the gain is twice as much.

So the above diagram is total cobblers, for one thing it's the CCS that makes it unstable. So it's back to the basic method with simple resistors and thermistors.

Then finally (cos of "interruptions") got around to boosting the gain, the input has to be a double stage with two transistors.

Cock up #2. ~ the OC44 isn't, it's supposed to be OC84. OC44 is only 40mW so would've blown up anyway. :shock:

This is all academic now anyway as I've redone it using AC127/AC128. The OC84's have been moved to the tone control input pre-amp.



 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#73

Post by Mike H »

Seems I haven't bunged up the latest schematic of this, so here it is.

Interestingly, the basic input / driver arangement is virtually as per the Transis-tronics phono pre-amp I copied!
Attachments
Transis-Tronics Pwr-amp-12.gif
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#74

Post by brig001 »

Mike, just thinking about my Class A from scrap project and using capacitors like you have to make an artificial zero like you have. I noticed that you don't reference your input and feedback to this - is there a reason for this?

Brian.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#75

Post by Mike H »

Yes, there's a transformer in the way :lol:


Ergo, strictly AC coupled only

Actually, using 2 caps in series like that was a bit of a fad in the DIY rags about late '70's, the idea is it:

A. provides additional power supply capacitance

B. provides AC coupling to 'ground' for the load

C. 'cause it's starts up at half supply potential (subsequently charged to whatever the DC of the o/p point is), you don't get that massive THUMP! at switch on. Well a little one maybe, but not so alarming.

D. allows smaller values for each, which may be more readily available for whatever reason, as it works as 2 in parallel.

However I also discovered, and don't remember anyone mentioning it at the time, and it's difficult to observe without something like spice :D is that:

E. most of the load current comes from the charge on those capacitors. The top half discharges the top cap through the load (and partially charges the bottom), and vice versa. The supply just provides about one third of the load current to keep the caps topped up. Unexpected that was but means mains transformer doesn't have to be huge, about 2A capability is plenty I reckon.

F. there is no F (© Andrew Ivimey) :D
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Post Reply