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21
The Newcomer's Forum / Re: Heathkit TA16
« Last post by GlenF on May 09, 2019, 10:23:02 PM »
Before I start to take readings, there is alot of brownish stains on the outside of the solder.  Is this exess flux, and could this be part of the problem?
22
The Newcomer's Forum / Re: Heathkit TA16
« Last post by Jazz P Bass on May 09, 2019, 11:03:33 AM »
Yes, the unit must be plugged into the wall outlet.
Power switch On.

Keep in mind you are measuring dc voltages.
So your meter must be set to read Volts dc.
23
The Newcomer's Forum / Re: Heathkit TA16
« Last post by GlenF on May 08, 2019, 08:33:59 PM »
I have the board out of the amp right now.  To do the tests, do I need to have it plugged into the wall so that there is power to the board or can I do the tests unplugged?
24
The Newcomer's Forum / Re: Heathkit TA16
« Last post by phatt on May 08, 2019, 07:34:10 AM »
Hi Glen,
         Yes hard to know where to start but *JazzBass* means disconnect the speaker,,  the Amp drives a load which is the speaker. Load is tek talk for the speaker. ;)
Assuming you have a meter,, set it to the highest DC voltage.

With speaker disconnected probe the output speaker terminals/wires and it should be very close to Zero VDC less than 0.5VDC.
Now with Ground probe on chassis the first DC supply is found at the output of the Bridge rectifier. (Marked G)  The rectifier is those 4 diodes marked D102 to D105.

(J) is common or ground and often also connected to Chassis but not always.

The voltages are on the schematic,, if not sure where they are on the circuit then often the Electrolytic caps will give you a clue as to where to find those voltage nodes.
they will not read Exactly the same but as long as they read close it's all good.

Some old amp layouts are quite dangerous so be aware of the mains input wires it can KILL you.  8|
 I Cover any bare terminals that hold mains voltages when I have to work on that stuff.
Phil.
25
The Newcomer's Forum / Re: Heathkit TA16
« Last post by Jazz P Bass on May 07, 2019, 11:34:33 AM »
"So you will have to muddle through and possibly trace out and draw sections that are in question."
26
Schematics and Layouts / Re: Dual or Split supply Audio amps
« Last post by phatt on May 07, 2019, 05:11:13 AM »
Be aware as there are caveats on the full power option.  xP
The novice might miss the limitations of using 30-0-30VDC supply rails.
You will likely blow the chip if you use a 4 Ohm speaker. (it's written in the specs)

This is a small chip with small surface area and the laws of fizzy stuff tells you it cannot dissipate the heat required to run 4 Ohms at high rail voltages.
so 25 Volt rails is a good safe option. 8|
If you want more grunt then you need a bigger Amp that can dissipate the heat.
Phil.
27
Preamps and Effects / Re: implementing presets
« Last post by jon_bondy on May 05, 2019, 08:53:46 PM »
@Jazz P Bass:

What do you mean by "it will take a lot more than simple potentiometer changes to get useful presets"?  Can you give me a few examples?
28
The Newcomer's Forum / Re: Heathkit TA16
« Last post by GlenF on May 05, 2019, 04:10:06 PM »
I'm not sure where the +38Vdc rail is, and how do I remove the speaker load?  I'm not an electrician, but I want to learn more about these things.
29
The Newcomer's Forum / Re: Heathkit TA16
« Last post by Jazz P Bass on May 05, 2019, 03:12:17 PM »
Ok. The lamp is lit.
That means you have voltage on the secondary of the power transformer.
Your next step is to verify the dc supplies.
there are 5 of them.
I would start at the +38Vdc rail.

A word of caution.
Being that this is a direct coupled power amplifier, I would advise removing the speaker load until you get things sorted out.
30
Preamps and Effects / Re: implementing presets
« Last post by Jazz P Bass on May 05, 2019, 03:07:50 PM »
Sounds like a fun project.

Although it will take a lot more than simple potentiometer changes to get useful presets.
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