more.. Amp DIY • DIY • Ask Amp Man • Gear • Amps • Gear Blog • Upkeep • EL84 • Head • Tube Head • January 2012
Rick Hogue, a good friendof mine who owns GarrettPark Guitars in Annapolis,Maryland, recently acquired anolder Carlsbro amp head. Heloved its sound and asked me totake a look at it. It turns out hehas a black plexi-panel, 60-wattCarlsbro CS60TC, in verynice shape. In all the years I’vebeen servicing amps, this is thefirst time I’ve run across one ofthese, so I was curious. Carlsbroamps were built in Nottingham,England, and seem to be morerare in the USA than any otherBritish amp.
The Twilight Saga, which also includes New Moon, Eclipse, Breaking Dawn, The Short Second Life of Bree Tanner: An Eclipse Novella, and The Twilight Saga: The Official Illustrated Guide, has sold nearly 155 million copies worldwide. Carlsbro: Sidewinder: hfenikkogammavservice.pdf: 12/02/20: NIKKO Audio Gamma V hfenikkogammavservice.pdf: 1113 kB: 8: NIKKO: hfe nikko gamma v service: CarlsbroSidewinderUserManual.pdf: 22/03/16: User Manual for 60W valve guitar combo amplifier manufactured 1986-88: 1490 kB: 112: Carlsbro: Sidewinder: WiringMCi500HPS131-300-D0.
The amp has two discretechannels, Bass and Treble, eachwith a low- and high-levelinput. The amp’s only controlsare Volume, Treble, and Bassfor each channel, along with aglobal Top Cut knob. A powerswitch and pilot lamp round outthe front panel with the noticeablelack of a standby switch.The rear panel is very minimalas well. An AC socket, thatappears to have been changedfrom a British Bulgin to a USIEC jack, a voltage selector, acouple of speaker output jacksand an output impedance selectorwith 3.75, 7.5 and 15 Ωsettings. Definitely old-schoolBritish! Rick offered to let metake it back to the shop and seewhat made it tick.
Before I disassembled thisrarity, I decided to try it outfirst. Very nice—the CS60TCsounded open and percussivewith just the right balance ofclarity, growl, chime, and grit.Think plexi meets Hiwatt, witha tilt towards the latter. Whatit lacked in front-end gain, itmade up for in tone.
When I pulled the chassis,I didn’t see anything out of theordinary. So what makes thisamp sound the way it does? Thecathodes of both V1 and V2 use1k Ω resistors and 64 μf bypasscapacitors. Seeing that indicatedthere should probably be morefront-end gain than the ampwas delivering. A quick look atV1 revealed the first anomaly—someone had installed a 12AT7in this position. Accordingto this amp’s schematic, thepreamp tubes should be all12AX7s. A quick change tothe proper tube resulted in ..nothing more than a moderateincrease in gain.
The rear panel with its old-school British design.
Measuring the plate voltageshelped make sense of this. Theplates of V1 read approximately125V DC. High enough forthe tubes not to be “starved”and artificially distort, but lowenough to achieve less-thanmaximumgain. But this can’tbe the only reason the Carlsbrosounds the way it does. Whatelse would I find?
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Moving on to the phaseinverter, there seemed to benothing exceptional here, either.The only surprise was a 68kfeedback resistor. Generally, theoutput stage will be “cleaner”and have less apparent gainwhen a low value feedback resistoris used. This setup however,in this amp, seems to yield anice balance between clean andmean, depending on how hardthe amp is pushed.
I then took a look at theoutput stage to find out what’slurking under those EL34s. Thefirst thing I noticed was thatsomeone had added a 470 Ωresistor in series with the stock1k screen grid resistors. Thenet effect of this should be aslight drop in the DC voltage atthe screen grids, which wouldneither substantially affect theoutput power nor tone of theamp, but I decided to verifythis. Switching back to thestock 1k resistors did indeedincrease the output a minisculefour watts, and there was a veryslight difference in the tone.At higher volume settings, theamp had just a bit more fullnessto it, but at lower volumes, theamp sounded slightly better tome with the additional 470 Ωresistors in place. It had just abit more jangle. This remindedme of what I always tell customersregarding amp mods:“Whenever you change something,there’s always a tradeoff.”
I also saw the bias supplyhad been previously repaired.The value of the stock droppingresistor from the HT windingto the bias diode is 180k Ω.Someone, I’m sure doing thebest they could with the partson hand, elected to place three47k resistors in series (yielding a141k total value) to replace theunusual value 180k bias resistor.The result was that the biasvoltage rose from the schematic’sstated voltage of -35V DC to amuch greater -50V DC, causingthe amp to be substantiallyover-biased. Lowering the biasvoltage to the schematic’s levelremoved all the crossover distortionpresent in the outputsignal, but set the idle currentof the output tubes at around65 mA. This was a bit too highin this amp, in my opinion.Adjusting the bias resistor toa value of approximately 160kplaced the tubes at a morerespectable 40 mA of idle currentand definitely improved theamp’s overdriven characteristicsat higher volume levels. Chalkup another validation for properlybiasing output tubes!
Well, there you have it—hopeyou enjoyed our tour inside arare and fine-sounding amp.
Carlsbro Eclipse 12 Manual 2017
Jeff Bober is one ofthe godfathers of thelow-wattage amp revolution,co-founded and wasthe principal designer forBudda Amplification. Jeff recently launched EASTAmplification, and he can be reached [email protected].4th December 2014
Gear Maniac
Carlsbro Eclipse 12 Manual 2017
Hi Guys,
I have a Carlsbro Eclipse 12 Powered mixer that was given to me faulty. As its digital i struggle to troubleshoot these problems rather than seeing something physical that is broken.
The amp just keeps saying 'REVERB CLIPPING' and the meters are maxed out on the master.
Has anyone had this problem?
Also, if no one knows how to fix this, is there any ideas on how I can re use it in some way? - One idea being a midi controller/Mixer?
Look forward to your feedback as I'm stuck with this one.
I have a Carlsbro Eclipse 12 Powered mixer that was given to me faulty. As its digital i struggle to troubleshoot these problems rather than seeing something physical that is broken.
The amp just keeps saying 'REVERB CLIPPING' and the meters are maxed out on the master.
Has anyone had this problem?
Also, if no one knows how to fix this, is there any ideas on how I can re use it in some way? - One idea being a midi controller/Mixer?
Look forward to your feedback as I'm stuck with this one.
Carlsbro Eclipse 12 Manual 2016
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