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Messages - tonyharker

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Amplifier Discussion / Re: Peavey Tmax-Where to start?
« on: May 24, 2021, 02:13:50 PM »
Often when an output device goes short it can affect the driver transistor in this case the 15031. Dont remove it just keep an eye on it when youve replaced the faulty output. BTW here's a link to a Peavey transistor list of equivalents.

Amplifier Discussion / Re: Peavey Tmax-Where to start?
« on: May 23, 2021, 09:52:50 AM »
The Peavey T-max appears to be hybrid with a Solid State power amplifier.  If it's a loud humm not affected by the volume control, disconnect the speaker immediately or it will be destroyed, and check for DC on the output terminals. If DC is present more than a few millivolts, then it is likely one or more output devices haxe expired.  You will need a schematic diagram and a conversion table for the proprietary codes Peavy use for their semiconductors.

(edited to correct typo)

Amplifier Discussion / Re: 200 watt amplifier board.
« on: May 22, 2021, 04:18:11 PM »
As I dont know where in Australia Rod lives, I can only use the information displayed on his web site and that is what he quotes. UK VAT must also be added (20%) and also the local Royal Mail charge for collecting this from me. This is not known but Rod estimates it at about £8.00. The P68 board costs US$32 (£22 approx). Unfortunately I am not prepared to pay this for one board no matter how good, even though the ones I have used before are certainly good quality.

Amplifier Discussion / Re: 200 watt amplifier board.
« on: May 22, 2021, 01:57:38 PM »
Yes I know about Rod and have already used a number of his boards, but I am not prepared to pay his ridiculous shipping charges of US$24.50 from Oz to UK for a board when all he has to do is stick it in an envelope.

Amplifier Discussion / 200 watt amplifier board.
« on: May 21, 2021, 02:00:21 PM »
Looking for a suitable project to build for a bass amplifier, I found this board (bare PCB) on Ali Express . . Does anyone know anything about it, especially the schematic as one is not supplied, only giving component values on the board? Has anyone bought and assembled it?


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?

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