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Circuit differences K200 and K250 heads? [message #27980] Thu, 04 February 2021 19:23 Go to next message
daveobergoenner@gmail.com is currently offline  daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri
Senior Member
I've never had a K250 head.

I currently have a K200, which has been re-capped, and the PS caps etc upgraded.
Through the 70's, I played a K400 into a pair of 3x15 CTS cabs. That's basically two K200's with a common power supply.
So, my knowledge base is almost exclusively the K200 designs.

Lately I've been considering a K250 head. Of course it would get a full re-cap, and similar PS upgrades to what I've done to my K200.

What I'm wondering is, what were the circuit improvements done to bump the power up from around 100 watts RMS into 4 ohms, to 125 watts into 4 ohms on the K250? Heavier power transformer? Stronger output devices? More of them? Higher PA voltages? I think the K250 was rated to drive 3 ohms...is that where the extra power came from?

My K200 now clips at about 115 watts into my 4 ohm bench load. It's a really strong amp. Will I really get much more from a K250 into the same 4 ohm cab?

Thanks,
Dave O.


Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
Re: Circuit differences K200 and K250 heads? [message #27981 is a reply to message #27980] Fri, 05 February 2021 09:32 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4739
Registered: June 2004
Location: NY
Senior Member
The biggest plus the metal face K150 and K250 amps have is far more flexible tone circuits in each preamp , less hiss due to IC Chips and FETs being used and a return to high and low gain inputs in each channel.

The additional wattage they have only shows up in the non effects amps since these semiconductors I mentioned above draw a tad less current then all the Transistors that are in a non effects K200.

The power supply voltage is the same between the 200B , k150s and K250s.

One other nice thing about these metal face amps is the output jack labeled "power module "that was ment to drive a power amp that made up the K500 two cabinet set up's.
This can be used to drive any power additional power amp in fact and is taken off at a different part of the circuit then the RCA jack on the rear of the K200B heads.

Also these heads have a record output jack that is padded down off of the speaker output jack so it gets the full tone of the amp fed out of it.

The other really nice thing about the metal face amps is that they have a reverb pan lock on the rear of the amp so pan failure is a rare thing!

The K250s where made to drive a 4 ohm load just like the 200A models and the 200B models.

[Updated on: Fri, 05 February 2021 09:45]

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Re: Circuit differences K200 and K250 heads? [message #27983 is a reply to message #27980] Fri, 05 February 2021 13:13 Go to previous messageGo to next message
sunnhead is currently offline  sunnhead
Messages: 221
Registered: June 2010
Location: Minnesota
Senior Member

250's for bass are the bomb. I use a 250 when giging. If with guitar the 250 is a great amp. It doesn't have the sex appeal of the plexi amps, so most folks stick to the 200 amps. BUT the coolest part of these is all the effects are on one channel like the 200A series. So many cool things you can do! Also, I have never recapped any of my amps, and I gig with them with out any issue.. just a thought, if it isnt broke dont mess with it!

-S
Re: Circuit differences K200 and K250 heads? [message #27985 is a reply to message #27980] Fri, 05 February 2021 18:54 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4739
Registered: June 2004
Location: NY
Senior Member
The more you use the amp the better in terms of cap life, also the most stressful time for a SS amp is the surge of voltage at turn on, the less of these the better, to the point that I was bringing a variance to gigs with me to run my amp off of!

[Updated on: Fri, 05 February 2021 18:56]

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Re: Circuit differences K200 and K250 heads? [message #27998 is a reply to message #27980] Mon, 08 February 2021 21:55 Go to previous message
daveobergoenner@gmail.com is currently offline  daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri
Senior Member
Thanks everyone!

I do most of my tone shaping with the Ampeg SCR-DI that I use ahead of the amp anyway. So, it sounds like there wouldn't be much of an advantage to me "upgrading" from my K200 to a 250. Sounds like both amps deliver about the same amount of power at clipping into a similar load.

My K200 is actually pretty quiet since replacing all the transistors in the preamps and the summing amp board. It's surprising how much better the newer silicon is. I also added an FET buffer on one input channel, so if I plug in direct, the really low input Z doesn't load-down my passive basses.

Thanks again,
Dave O.


Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
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