I have a HK Citation II that has been converted to monoblocks. Over a period of time, one channel starts popping, like a plate pop, after the unit warms up. We switched tubes, replaced resistors that were getting hot to no avail. Any help would be appreciated.
There are photos of both here:
https://www.usaudiomart.com/details...kardan-citation-ii-mono-blocks-sell-or-trade/
There are photos of both here:
https://www.usaudiomart.com/details...kardan-citation-ii-mono-blocks-sell-or-trade/
I rebuilt my HK Cit II about 5 years ago and I do not recognize the transistor on the heatsink on the lower left on the turret board.
My amp has has no silicon. This picture.
https://www.usaudiomart.com/details...-ii-mono-blocks-sell-or-trade/images/3824041/
My amp has has no silicon. This picture.
https://www.usaudiomart.com/details...-ii-mono-blocks-sell-or-trade/images/3824041/
Converting a stereo amplifier to be a monoblock requires some very tricky modifications, and special care.
Without extensive work to draw up an accurate schematic of the amplifier circuit that you now own, it will be even more difficult to troubleshoot.
Depending on the modifications, it might become an oscillator (did you check with a scope to see if it is oscillating)?
Because you have 4 6550 or 4 KT88 tubes, and the output transformers, etc. all "tied together" in one fashion or other, it will be more difficult to troubleshoot than if it was still a stereo amplifier with two independent channels.
Are you using KT88 tubes?
Are you using 6550 tubes?
Are they of good quality?
One of those two tube types is generally more likely to have thermal run-away, or other problems if the resistance to ground of g1 circuit is too high.
Without extensive work to draw up an accurate schematic of the amplifier circuit that you now own, it will be even more difficult to troubleshoot.
Depending on the modifications, it might become an oscillator (did you check with a scope to see if it is oscillating)?
Because you have 4 6550 or 4 KT88 tubes, and the output transformers, etc. all "tied together" in one fashion or other, it will be more difficult to troubleshoot than if it was still a stereo amplifier with two independent channels.
Are you using KT88 tubes?
Are you using 6550 tubes?
Are they of good quality?
One of those two tube types is generally more likely to have thermal run-away, or other problems if the resistance to ground of g1 circuit is too high.
Agreed, this is certainly no longer a HK Citation II.
Post all the schematics, DC voltage readings, and close photos.
Post all the schematics, DC voltage readings, and close photos.
These amps was built by Justin Weber (ampsandsound.com) as a design prototype for his amplifier. His tech guys know what they are doing.
https://ampsandsound.com/collections/2-channel-amplifiers/products/zions-monos
He thought that the sound is coming from the aftermarket power conditioning circuit that was installed at sometime and he left in place. My tech is emailing Justin about that. The other amp is really quiet, and is an exact duplicate of the problem amp.
Justin’s description:
All original Cit II circuit with original turrets. All original output transformers.
The donor amp had a power transformer fail. As such we used the rare and original output transformers. By using the original Channel turret boards and output the amps maintain the sonic purity of the originals but are more reliable and usable now.
Power transformers are from Heyboer and closely match the orig HK Spec. Chokes are Hammond.
Separate power supplies increased output to 65watts RMS. Bandwidth is unbelievable 4hz to 115khz @ 1 watt, 10hz to 110hz @ 10 watts."
https://ampsandsound.com/collections/2-channel-amplifiers/products/zions-monos
He thought that the sound is coming from the aftermarket power conditioning circuit that was installed at sometime and he left in place. My tech is emailing Justin about that. The other amp is really quiet, and is an exact duplicate of the problem amp.
Justin’s description:
All original Cit II circuit with original turrets. All original output transformers.
The donor amp had a power transformer fail. As such we used the rare and original output transformers. By using the original Channel turret boards and output the amps maintain the sonic purity of the originals but are more reliable and usable now.
Power transformers are from Heyboer and closely match the orig HK Spec. Chokes are Hammond.
Separate power supplies increased output to 65watts RMS. Bandwidth is unbelievable 4hz to 115khz @ 1 watt, 10hz to 110hz @ 10 watts."
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The link on Post # 5 does not show any amplifier that has 4 power output tubes.
Might be the same engineer, but not anything like a Citation II converted to a mono-block.
Might be the same engineer, but not anything like a Citation II converted to a mono-block.
I've seen the 4u7F electrolytic bypassing the input valve's G2 cause intermittent noises. Today these are replaced with an MPP like a Solen. Repaired one for a friend within the past year. Getting to them is Zero Fun.
All good fortune,
Chris
All good fortune,
Chris
Let's assume that each is simply one half of a Citation II. With the exception of the power supply, they were two individual amps on one chassis when stock. They actually did have separate filament windings for each channel.
Since the OP's are clearly not using 6L6 tubes, they must be the Cit II circuitry as well. They are using the Cit II boards.
Mentioning the guy who built them was just a distraction.......
At any rate, if you had an O-scope, I wouldn't think this would be too hard to troubleshoot.
Since the OP's are clearly not using 6L6 tubes, they must be the Cit II circuitry as well. They are using the Cit II boards.
Mentioning the guy who built them was just a distraction.......
At any rate, if you had an O-scope, I wouldn't think this would be too hard to troubleshoot.
I did’t mean to distract with the builder, but I thought it would give credence to where they came from, but you are correct. My tech person in a small town needs leads to point him in the right direction, and I just want to help get my beautiful sounding amps back. That said, thanks for the advice so far, and anything that can help is certainly appreciated.
It was an interesting distraction though.
I hope your tech figures it out and fingers crossed it’s something simple.
I hope your tech figures it out and fingers crossed it’s something simple.
You could try recording the sound and posting that. Pictures under the chassis help. Has your tech tried to prod around with an insulated stick to try and induce the noise and see if there is a mechanical issue?
I went by the shop today. He uses a Sharpie to prod around. He will put it on the bench soon to record the light popping sound. I will take pics then. Thanks all for the help!
