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Just got a G-K 400 RB-MKii !!!

ReneB

ReneB

Guest
Dec 6, 2014
219
187
Ithaca, NY
#1
Yes I'm excited :hyper:

I've been reading and asking questions and although I thought I'd end up with something smaller, this seemed like a great deal especially considering it comes in a nice case too.

Is there anything I should know about the care and feeding of an older model, 400RB? I can't find it now, but when I was doing my research I stumbled upon a post (on here I believe) that mentioned replacing the op amps in this unit. Also, I read somewhere about adjusting the bias of the amp. Anyone know where I can find info on doing that?

Here are some pics of the amp and rack case ... how'd I do?

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#2
If you PM me (start a conversation) with an email address I have a service manual in .pdf. The opamp IC's don't need to be changed unless you have excessive hiss, low gain, non-functional eq. The series II has a removable power cord and later production had the newer switch IC for the boost circuit. The original boost switch IC became obsolete.

Care and feeding; Clean the pots and switches every few years and keep the heatsink fins on the back clean and unobstructed :). Power supply caps may need replacement (electrolytic caps in those days were good for 15 to 25 years).
 
#6
I noticed that this series of 400 RB is up to IV, now. Was there any one series that was more popular with bass players than another ?
 
#7
Just remembered to answer a question from the PM with ReneB that would be best answered here anyway.
Series change notations from G-K denote "major" changes. The series II's was a revision for CSA approval (removable power cord). Series III was a mechanical update with a power increase, series IV voicing change and further power output increase.
 
#8
I was wondering the same thing as @jnewmark asked when I was looking. Hopefully B-String will correct this if I'm wrong, but when I was looking at these units, I noted that the earlier ones (I & II) definitely had a more 'tank-like' exterior build quality and version III seemed similar, whereas the latest IV, seems a bit less robust at least by outward appearance. That said, they don't seem to be particularly heavy. I think even the older ones run at about 14 pounds. As for sound, I have NO idea.
 
#11
Mystic Michael said:
If I'm not mistaken, isn't bias adjustment something that is exclusive to tube amps? I've never heard of it being relevant to solid state amps.

MM
Click to expand...

No, it is an amplifier operating class that determines the need for bias. Tube or SS devices must be biased above cut-off (non-conducting) in class AB, G or H. Class A biases the device in the center of it's operating range.
 
#12
I don't know much if anything about bass amps, but older hi fi solid state amplifiers (e.g. Yamaha, Marantz, etc.) do have bias adjustments. From my limited understanding, it affects the efficiency and performance of the amplifier. I've adjusted a few pieces of gear myself. Usually this info is found in a service manual.
 
#13
B-string said:
Just remembered to answer a question from the PM with ReneB that would be best answered here anyway.
Series change notations from G-K denote "major" changes. The series II's was a revision for CSA approval (removable power cord). Series III was a mechanical update with a power increase, series IV voicing change and further power output increase.
Click to expand...

So, it seems like a deliberate change in " tone " ( voicing )was done in the series IV. Anyone care to comment on the difference ?
 

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