The Amp Garage

Hi there. I would like to know if there is a safe way to switch between 2 guitar cabinets? I'm using a 60W tube (fender style amp) and I would like to build an A/B (or even A+B) switcher box to chose between 2 cabinets (Both 8 ohm). I know the Radial box but it's way too expensive for me. I've heard...

Thanks Tubeswell for the attachment. Great insight man. Really valuable information. I'll read it carefully and I will test the coupling caps.
Thanks everybody for the advice. It's really helpful since I'm new to the world of amplifier servicing.

Thanks pdf64 for the help. No change on readings without the P.I v6 (what LTP stands for?) . Very good idea to take out the whole NFB - P.I. circuit. No change from a distance of about 1m. from the preamp. The meter is in excellent condition. The probe must be defected. I may have destroyed it, by m...

Thank you guys for the great help. It was a problem with the bias probe. Absolutely unreliable. I did a test measurement across a 100Ω 1/2watt resistor on pin 8 and it seems the bias circuits is working well. I take a reading of 4.5V which means 45mA x 100. 45mA is what I'm looking for. I will chang...

Hi Firestorm. Thanks for the reply. I don't think there is a problem with the diode. Everything works well with the circuit. The problem must be either with the bias probe and the bias method I'm using or with a capacitor or something somewhere around the P.I. - NFB.

Thanks again for the help guys. I'm not experienced on working an amp so your help is much appreciated. Xtian, the problem occurs to both tubes even when I approach 40% dissipation (assuming the readings are correct and there is no problem with the probe). So I guess there is no real matching proble...

My bias probe is similar to this one: https://www.amazon.com/Eurotubes-Bias-P ... B019PAVXPG

My mistake. It juest measures current, no voltage. I measure plate voltage on pin 3.

Hi pdf64. Thanks for the interest. I 've got a "proper" bias probe- It has worked well in moste cases. So I just plug it in the socket and it goes to my meter I measure plate current mA. I'm aiming for this current, because I've already measured plate voltage and I know thetube plate dissipation. I ...

Sorry about that. I mean to place a But I'm scared to place a 25k ohm in order to raise the bias value to the range of 40-50mA. Cheers

My plate voltage is aroun 430v with the tubes pluged and around 470v with the tubes unplugged. They are simple electro harmonix 6l6 (I think they are 30w max). Usually two of them. In an amp made for 4. Placed in sockets 1 and 3. I'm aiming for 42-47mA. When I placed the 15k ohm/5 watt resistor (whe...

Thank you Xtian for the quick and kind reply. Here's another picture of the bias- rectifier board and the bias pot https://imgur.com/a/BdqaD My experience is pretty basic. Just a basic renovation job on pedals and new to the amps world but I ve spent quite some time on this particular project. This ...

Hello kind people of the forum. It's the first time I'm writing. I've got a mid 70s Acousta amplifier (silverface Twin reverb replica). I'm trying to blackface it. Most things go well. bThe rectifier is a bridge rectifier because of the Power Transformer. It hasn't got a normal channel. There was an...