Hartke HA3500 valve preamp no output

[neepheid]

Hi there

I've acquired a Hartke HA3500 head recently, but there's no output from the valve preamp - SS preamp is working. Valve is glowing slightly, the pot that controls the valve preamp seems a little loose - and that's about where my troubleshooting powers end

Can you give me any pointers as to where to look to try and narrow down this problem?

Thanks

Matt

[lowell]

hey,
are you multimeter handy? you need to tighten up that pot first... then look closely around the tube for any other loose connections or fried parts. Use a chopstick or sharpie to poke around cause some loose connections might not be very visible till you poke them. then use a tube voltage chart check each pin DC voltage. connect the black to ground/chassis. You should get something AROUND these figures:

pin 1=200v
pin 2=0v
pin3=1.5-5v
pin 4&5=heater (switch meter to ac volts to read this... should be around 6.4VAC
pin 6,7, and 8 should read just like 1,2, and 3 or have zero reading if this half of the tube is not being used.
pin 9=heater (might read 6.3VAC might read 0)

You can also set your meter to AC volts on the lowest setting or second to lowest setting. then plug in your bass. black meter lead to ground and red meter lead to pin 1 or 3... try both. play a note and see if the meter reads anything. that will tell you if the tube is putting out your bass's signal as it should. it will be pin 1 or pin 3 depending on if the tube is wired as a typical gain stage(pin 1) or a cathode follower (pin 3).

get back w/ results

[Enzo]

I would poke at each of the various film caps in the area of the tube with a chopstick to see if any of them has a broken lead.

[neepheid]

Thanks for the pointers, I wasn't expecting a reply so soon. Going on holiday on Friday for 2 weeks. Just don't want to leave you hanging. Will get back to you when I get back!

[neepheid]

Managed to fix it - a burned out resistor was stopping 200V getting to the valve. Between your initial pointers and the schematics me and a mate worked it out and replaced the dud resistor (R407 to be exact).

Thanks for the assistance.