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Messages - tonyharker

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As far as I can see these Nu-tubes are just a gimmick. You dont get a lot of gain from them so they are not going to have much effect to the signal.  Snake oil :)

Amplifier Discussion / Z-MATCHER 100W IMPEDANCE MATCHER
« on: September 13, 2019, 05:42:51 AM »
Does anyone here use this device, any comments and does anyone know what is inside? It looks small to house a 100w transformer.

Amplifier Discussion / Re: What Op Amp for 20W+ Busking Amp?
« on: August 08, 2019, 05:36:53 AM »
Check out the OEP30w amplifier this will give you 17w into 2x8 ohm speakers in parallel at 12v.  Class d bridged amplifier, you wont hear the difference between 17 and 20w. All over ebay at about $2

Amplifier Discussion / Re: Fuse or resistor?
« on: June 19, 2019, 05:10:50 AM »
The resistor within a circle /oval is the symbol for a thermistor, and is part of the temperature compensation for the bias network. It should - but is not always - be mounted on the heatsink for the output transistors. Unfortunately there is no value given for it.

It doesnt really matter. Any dual op amp eg TL072, NE5532, JRC4558 etc will work.

Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: March 02, 2019, 07:01:46 AM »
Probably something simple like a dry joint or a duff pot

Amplifier Discussion / Re: Polytone 102 Tremolo
« on: January 24, 2019, 02:37:54 PM »
The symbol is the Greek letter Lamda which indicates the resistor is light dependent. The resistor in a circle above R53 must be a light source (48v lamp?).  This is coupled optically to R16 which is a Light dependant resistor. 

Amplifier Discussion / Re: OK to run Marshall Lead 12 into 4 ohm load?
« on: November 26, 2018, 06:15:00 AM »
The output transistors are ok with the higher power, but the heatsinks are a little small.
All I can suggest is try it and see how hot it gets.  If you cannot hold your fingers on the heatsinks for a couple of seconds then they're too hot.

Amplifier Discussion / Re: SWR 550X Bass Amp Trouble
« on: September 21, 2018, 06:21:57 AM »
The first thing I would do is to check the output for DC. To me it sounds like one of the output transistors has failed.

You will have blown the power amplifier by connecting the external amplifier. It will be an IC or discrete transistor device.  A photo will show which.  If an IC it will probably easier to replace if you are competant to do that - can solder properly etc. A Transistor amp will be more complicated. If you are not sure it would be better to take it to a tech.

Amplifier Discussion / Re: Repairing a Roland JC-50
« on: June 25, 2018, 01:42:32 PM »
Power transistors, and driver transistors are in the top right of the schematic page 3, Q18, Q22, Q27 & Q28 for later serial numbers, 25xxxx or Q11, Q12, Q13, & Q14 on page 7, for earlier serial numbers 24xxxx. The box around Q13, Q14, Q27 & Q28 means they are on a heatsink or mounted on the chassis

Amplifier Discussion / Re: Sunn Coliseum 300 Issue
« on: June 09, 2018, 06:35:19 AM »
First thing clean both Send and Return jacks and try again.

Amplifier Discussion / Re: Hohner Pianet Amplifier Low Output
« on: May 30, 2018, 01:35:32 PM »
Glad to hear it. Enjoy playing.

Tubes and Hybrids / Re: Tube shields on EL-84's
« on: May 08, 2018, 05:17:18 AM »
Don't use shields on power tubes like EL84s, you will only shorten their life and maybe overheat them.  Shields should only be used in preamp tubes where they are likely to pickup RF.  So hi gain hi impedance first stage amplifier tubes only. Tube retainers ie spring clips can be used on any stage.

Amplifier Discussion / Re: Hohner Pianet Amplifier Low Output
« on: April 24, 2018, 10:35:34 AM »
Yes, although putting  7v  approx across the speakers doesn't seem right.  Try biasing at a lower voltage first say 3v and see what it sounds like. Do you know what power the speakers are?

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