Resitor replacement and power rating.

[dimdom]

Hi Guys,
I have a Hughes & Kettner ATS Sixty. Schaltplan-ATS60-Sixty(1).pdfSchaltplan-ATS60-Sixty(1).pdf

R35 (located on plate supply) has been getting rather warm and smokey. This is also apparant from the discolouration. I am replacing the x2 15uF 450v smoothing caps. I would also like to replace this resitor but i'm not 100% It's wattage.

Im unsure of my maths but I reckon a max of 5W, that is based on the plate being short thus drwaing max current.

Any advice or confirmation would be much appreciated.

P.S i am new to this forum and so far it's what i've been missing!!

Cheers

Dom

[pdf64]

Yes 5 watts should be plenty, overkill in a good way, if it will fit?
The other key specs are voltage rating - at least 360V, and flameproof/retardant.
The big question is why is it getting hot?
What's the voltage either side of it?
Is the mains connected to the 220V power transformer (should be 240V!)?
Pete.

[dimdom]

Hi,
Thanks for replying. The voltage across it is 360V. I think it was getting hot, due to a leaky capacitor. I am replacing those, as It was getting hot without the 12ax7 in situ.

Hoping to have it back up and running very soon. Although as it is approx 20 years old I am going to replace all the electrolytic's.

Was thinking of a speaker upgrade eventually too, but that's on the back burner for now.


Cheers

Dom

[dimdom]

Guys,
i am having more woes with this amp. The clean channel works fine, but the overdrive channel does not work at all. It appears there is not the required 360v plate voltage being supplied from the transformer. It appears there is only approx 240-260v. I have disconencted the secondary from the PCB and measured the value.

I had previously connected a 15uF filter cap the wrong polarity doh and a 27kOhm in series resistor started to smoke alot, thats when I realised my mistake!

Have I damaged the Transformer?

Any help or advice appreciated.

Cheers

Dom

[pdf64]

The high voltage transformer secondary is protected by its own fuse, so should be ok.
Did you replace the cap or just refit it the right way around?

[dimdom]

Hi PDF64,
I simply re-fitted in the correct polarity. Could I have possibly caused one or more of the diodes on the rectifier to go S/C or O/C. They are only bog standard 1N4007's wich I have to hand and can replace this evening.

I am was just concerned that I only measured approx 240-260v when that part of the transformer was disconnected.

Kind Regards

Dom

[pdf64]

Need to replace the cap really, they're only specified for 0.5V reverse voltage usually! You're lucky it didn't explode and spurt its innerds out!
Which cap is this? The reservior cap (no part ref) after the rectifier, or C17 after the 27k?
Where are you measuring 260V? Is this with the valve fitted?
Assuming that a 50mA fuse was fitted, it should have blown before the diodes popped.
Does you meter have a diode tester?
The failure mode would likely be a short, so you could check the diodes for that in circuit.
PCBs tend to be rather delicate and it's easy to accidentally lift a track unless you're super careful, so best not to mess with replacing diodes unless you have to. Otherwise I'd say just replace them.
Pete.

[dimdom]

Hi Pete,
Sorry about the lack of response, I have had a very busy couple of weeks. I repalced all four bridge diodes. When the two 15uF caps are removed from the circuit the amp does not blow the 50mA therefore I know all is ok up to the 27k resistor.

I suspect as you do that I have damaged one or both of those caps. I will order replacements and let you know what happens.

Kind Regards

Dom

[dimdom]

After replacing the caps again, I still had no o/p from my overdriven channel. At this point I was pretty frustrated and fed up. So I decided to take the amp to a local repair shop. 2 weeks later after returning from being out of the country on business. I recived my amp back from the the repair shop in working order! yey!


However my Euphoria was short lived, over the weekend, whilst I had the house to myself and the neighours were away, I took the opportunity to crank her up and see what she sounded like, the answer was very loud for a short period of time. Then there was a popping and crackling sound, and a very sorry sounding quiet amp!!!!!

My first guess is I have damaged my speaker, it is an 8Ohm 100watt original speaker, so approx 20years old. I will try the old trick of putting a 9V battery across the speaker terminals to see how the speaker sounds.

Any ideas welcome.

Cheers

Dom

[pdf64]

Can you try the amp through another speaker and another amp through that speaker (a friend's amp)?
If not see the 'checking a speaker' option in Celestion | Guitar Loudspeakers
A 100W speakers should cope with everything that a 60W amp can put out.
Pete.

[dimdom]

Hi Pete,
I have checked the resistance of the speaker, = 6.5 Ohms
Used a 9.5v battery to check the movement of the speaker, it does sound a bit scratchy..?

I don't have another amp of a friends amp to verify either the speaker or the amp.

Wondering If I could stick a sig gen on the speaker?!?

Perhaps I should be looking beyond the speaker and into the amp.

Cheers

Dom

[Enzo]

A 9v battery will tell you if a speaker works or not, but won;t help tell you how it sounds, at least not very much.

Unless your signal generator is on steroids, it won;t drive a speaker. You could connect the speaker to a home stereo for test.

6.5 ohms DC resistance is pretty typical for an 8 ohm impedance speaker.

[dimdom]

After further inspection, I have found that the speaker has very very little defelction in it. maybe just a couple of mm in either direction, and when it is moved it makes a scraping noise.

when I removed the cloth from the panel the speaker is mounted in, I found that the cloth had been put back with some regular normal size stationary staples as opposed to the larger/stronger upholstery staples. There was also some bluetac like material around the edge of of the speaker?!?!?

So it seems I have to replace the speaker, now I have to make a decision on what speaker to get!?!?

I have attached some pics of the current suspect speaker.


Cheers

Dom

[jpiornos]

Excuse me, but Has got anybody the ATS 60 Schematic??. thanks : (

[mozwell]

ATS60 and ATS120 for reference
Check the headphone socket, you may be having a poor connection on the switch in the socket.