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Messages - tonyharker

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Tubes and Hybrids / Re: Reduce signal from preamp.
« on: January 21, 2021, 02:21:35 PM »
12a?7 valves have a 12v6 heater between pins 4 & 5 and a centre tap on pin 9. for 6.3 v common pins 5 & 6 and feed supply between these and pin 9.  AC or DC  doesn't matter.

Preamps and Effects / Piezo Preamp
« on: October 29, 2020, 05:14:43 PM »
 Has anyone tried to use one of those Piezo preamps sold for ukuleles like this on Ali Express on a magnetic pickup?

Guitar News / Re: More class D love - GPA-100 from Harley Benton
« on: September 30, 2020, 03:39:53 PM »
Something odd about this amp. The blurb here says '130 watts into 8 ohms or 210 watts into 4 ohms,' however the rear of the amp shows the power consumption - 230 v ~50Hz 0.6A which equals 138w . So how can you get 210 watts from a 138w supply >>100% efficiency. Even 130w from 138w is 94% just about achievable for Class D amplification.

Tubes and Hybrids / Re: VHT Classic 18 Preamp Modification
« on: September 21, 2020, 08:22:42 AM »
You have forgotten that the TL072 is a dual op-amp.  What does the other half do?

Schematics and Layouts / Re: Barcus Berry 1720 Power Transistors
« on: July 08, 2020, 06:07:12 AM »
Looking at the drive current through Q4 only 8mA approx, I would suggest that the output transistors are Darlington transistors, in which case 3055/2955s wouldn't be suitable. If they are TO3 cases try MJ11015 pnp and MJ11016 npn as replacements if you can get them.  If they are plastic types then TIP142 and TIP147 would work.

You appear to have some parts missing from your amplifier board. Including the input level pot. The g1xon is probably putting out too much volume for your amplifier so you will need someway of turning it down. What gain did you set for the LM386?

Is the hum affected by the volume/gain controls or is it there all the time. And is it LOUD.

Amplifier Discussion / Re: Complete Rookie
« on: May 07, 2020, 11:03:48 AM »
Also try C B Gitty, home of Cigar box guitars   877-470-5707


Did you remember to isolate the transistor tab from the heatsink?

The Artec amp uses this IC although they rate it at 2.5w.  The Electro Harmonix EHX 5MM Guitar Power Amplifier also uses this Chip.

Can I suggest NJM2073 bridged with JFET buffer a la Ruby or noisy cricket. NJM2073 gain is some 44dB or x158 approx. Probably enough gain for a big muff tone control after the buffer. NJM2073 will give some 2 watts into 16 ohms and about 1.5w in 8 ohms. Almost forgot - off 9v.

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

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