Help, diagnose limiter

[catch29]

Lamp limiter with 100w bulb. Plug in mono valve power amp (Heathkit ma12), signal and speaker connected. On power up limiter glows bright quickly then drops to nothing only to gradually glow up to 25% as valves warm up. No signal from speaker, slight background noise, valves all lit. What could be the culprit?. Be gentle with me, I'm new to this.

[Ed_Dinning]

Hi, probably nothing wrong with the amp; much more of a worry if it lights up brightly and stays that way.
You are now probably safe to plug the amp in direct to the mains.

I think there was a set of notes on the use of the limiter on the forum somewhere

Ed

[roadster]

The MA12 has a volume control next to the input socket, does the "background noise" alter when the volume control is adjusted?
They are quite a nice little amp; I have one in the workshop which normally has an Eddystone 820 tuner driving it but its main purpose is as a test amplifier.
Rod

[catch29]

Hi Rod. As a matter of interest, the last MA12 for sale on Ebay was a non worker with lots of missing components, Cap's, valves etc and went for well over £100!.

[Diabolical Artificer]

The first law of fault fault finding is "Thoult Shall Check Voltages" before that though, pop the amp upside down, pull the main fuse, is it the right current rating?

Second, pop the hood, have a good look inside, use all your senses, anything smell off, anything burnt of scorched? Next get a magnifying glass and have a closer look. It's the first thing I do with any new electronics that arrives, as Dave says,"don't turn it on, take it apart" after all, when you buy a car or a new wife the first thing you do is kick the the tyres or check her teeth. : )

Everything look ok? Power the DUT (device under test) on the Lamp Limiter (making sure the amp has a dummy load or test speaker attached ) , now, check voltages. First, get a pad of paper, write -
HT1 2 3 4 (meter on DC volts) HT1 = first big capacitor + terminal, carefull, high voltage. HT 2 = 2nd big cap after the big resistor. HT3 = next de-coupling stage or cap,etc.
Ripple 1 2 3 4 (meter on AC volts)

V1 a a V2 etc, etc. Or .....V1 pin 1) a
g g pin 2)g1
k k etc
Heaters V1 V2 etc (meter on AC)
Clip black meter test lead to ground or chassis, use red probe in right hand,left in pocket, scratching your head or picking your nose. All this should tell you what the amp is up to. Compare to a schematic, hopefully it will have voltages on it, if not if you have cathode voltage on V1, it should be working, same goes for all the other valves.

Andy.