Mk IV Questions

j beede wrote:i'd like to hear some details about those ribbon drivers Denny9167.

They are made by a company called BG,they stand around 6 1/2' tall, they have a range from 150Hz to 18,000Hz 400W max power handling. I am planning on a powered subwoofer to handle the low end.

Here is the link to the web page

www.bgcorp.com

also check www.partsexpress.com for more imformation. That is were I purchased mine.

One of the Bias caps showed some signs of chemical leakage, so I decided use Dynakit's Bias Circut Kit. It uses higher value and voltage caps with a IN4007 Diode replacing the green one and I choose carbon resistors for whatever reason.


New Transformer cover to match the other amp. In hindsight in may been a poor idea because the old covers were hard to get off and I think I was lucky not to damage the transformer. Plus the quad cap really needs to be uninsalled, but I able to get it on. Also the four corner holes do not match up, but that was no big deal because the center did.


Finally some matched 6CA7 electro-harmonix and a lot Flitz. I biased the tubes to 1.43. Think I am done for for now. Will need to read up on upgrades and start looking at the circuit board caps. Thanks all for the help and good ideas.

Sorry to be Mr. Spammy, but I was doing the Bias one my factory wired amp and had a question.


One this one I have pulled yellow green wire from pin 2 and noticed a jumper wire connecting pin 2 to pin 3.


Here is the kit wired one I just did, but there is no jumper between pins 2 and 3. The yellow and green wire just sits there doing nothing. The amp plays fine, but when I did the upgrade I did wonder why the wire would just sit there not connected to anything.

Looked like in the schematic it is jumpered any thoughts?

if you look at the schematic for the MK4 the yellow-green wire should be going to ground, it is the center-tap for the filament voltage

Thanks Tubes4hifi,

That makes sense, post 3 goes to ground. The kit amp showed no evidence of this being ever being installed. I should have questioned a transformer wire being soldered to a terminal that doesn't go to anywhere as suspect. Easy fix thanks again.

Little jumper installed. The PA-135 was running a lot hotter than the one on the other amp. With it grounded correctly they both run very cool now. That was going to be my next issue to figure out, so I'm glad it was an easy fix. Also moved to transformer leads to the lower terminals like the factory one.



Cage installed to protect it from Great Dane tail swipes.

very good! now enjoy!!