Jump to content
Gibson Brands Forums

Andyroid

Members
  • Content Count

    60
  • Joined

  • Last visited

Community Reputation

2 Neutral

About Andyroid

  • Rank
    Member
  1. THIS IS A REPLY POSTED TO THE BC30 MOD THREAD, I THOUGHT IT WOULD ALSO BE USEFUL HERE Hi, my previous post may be a little difficult to read, I've never been good at writing. So, I'll show you two schematics, the original, then the modded one. The first one shows the original power supply. The transformer secondaries (350-0-350) go to the 'Standby' switch and then to the main circuit board. These are relatively thin red wires that come from the power transformer, through a rubber grommet in the chassis and then go directly to the 'Standby' switch. The next schematic includes
  2. THIS IS A REPLY POSTED TO THE BC30 MOD THREAD, I THOUGHT IT WOULD ALSO BE USEFUL HERE Hi, my previous post may be a little difficult to read, I've never been good at writing. So, I'll show you two schematics, the original, then the modded one. The first one shows the original power supply. The transformer secondaries (350-0-350) go to the 'Standby' switch and then to the main circuit board. These are relatively thin red wires that come from the power transformer, through a rubber grommet in the chassis and then go directly to the 'Standby' switch. The next schematic includes
  3. Hi, my previous post may be a little difficult to read, I've never been good at writing. So, I'll show you two schematics, the original, then the modded one. The first one shows the original power supply. The transformer secondaries (350-0-350) go to the 'Standby' switch and then to the main circuit board. These are relatively thin red wires that come from the power transformer, through a rubber grommet in the chassis and then go directly to the 'Standby' switch. The next schematic includes the two new 68R resistors, the green arrows point to them. There is plenty of free spa
  4. I've just found another design flaw that may be the sole reason the BC30 self destructs. There is not enough limiting resistance before the rectifier. Limiting resistance helps keep ripple current within limits and is stated on the datasheet. It is worth noting that the choke will slightly lower the required limiting resistance, but not by much. The above datasheet chart provides the calculation necessary to determine the limiting resistance provided by the transformer: Rs = Rsec + N2Rpri I have measured Rpri to be 5.5R and Rsec to be 37.5R (75R for the entire winding) so...
  5. I've just found another design flaw that may be the sole reason the BC30 self destructs. There is not enough limiting resistance before the rectifier. Limiting resistance helps keep ripple current within limits and is stated on the datasheet. It is worth noting that the choke will slightly lower the required limiting resistance, but not by much. The above datasheet chart provides the calculation necessary to determine the limiting resistance provided by the transformer: Rs = Rsec + N2Rpri I have measured Rpri to be 5.5R and Rsec to be 37.5R (75R for the entire winding) so...
  6. I've just found another design flaw that may be the sole reason the BC30 self destructs. There is not enough limiting resistance before the rectifier. Limiting resistance helps keep ripple current within limits and is stated on the datasheet. It is worth noting that the choke will slightly lower the required limiting resistance, but not by much. The above datasheet chart provides the calculation necessary to determine the limiting resistance provided by the transformer: Rs = Rsec + N2Rpri I have measured Rpri to be 5.5R and Rsec to be 37.5R (75R for the entire winding) so...
  7. You say you turned something to get to the main fuse, that sounds like the HT fuse. There is also a 'master' fuse drawer built into the IEC(power) socket. I use a small flat screw driver to lever out the fuse drawer a bit like in this picture, only the BC30 one is much better, it also has a slot for a spare fuse and Epiphone will have included one! There are also seven different fuses on the actual circuit board inside the amp, I think about three of them are directly in line with the power transformer and could be to blame. BTW even with a silicone diode rectifier you only need standby to hel
  8. I've just turned my spare BC30 into a 50w bass amp with fixed bias, as the BC30 and SoCal use the same power transformer I thought I'd cheat and use the SoCal schematic to derive the bias supply. As this is my first fixed bias amp I just blindly followed the schematic and subsequently turned a capacitor into a firecracker! I was just about to lean over it to measure the bias voltage so I'm lucky it didn't blind me! I'm just posting this here in the hope I may save others from trouble when they recap their SoCals or whatever. Basically, the capacitors are the wrong way round in the schemati
  9. You must have used the standby switch. This amp is notorious for blowing fuses and rectifier valves because of the flyback voltage from the choke when the standby switch is flicked. Just replace the mains fuse (located in the power socket drawer) and check your rectifier, then leave the standby switch in 'Play' mode permanently. Don't worry, this kind of amp (it's a guitar amp, not radio transmitter) doesn't need a standby switch. Andy
  10. I've been recording for about 17 years now and building/selling gear in a music shop for about 6 years, most of my gear only gets used to record full live bands but the principles are kinda the same for bedroom stuff (only no need to worry about venue ambiance and mic phasing). Bedroom/home studio stuff that's one track at a time is easy to set up. All you need is a good dynamic mic for guitars (Shure SM57 is the industry standard) and a good condenser mic for vocals. Finding one that suits your voice can be a costly adventure but a great neutral-ish one I'd recommend is the MXL 2003A (NOT the
  11. I used modern Tung Sol 6V6GT. So they were operating way out of their league. I've heard the modern JJ/Tesla 6V6 would probably handle it but would sound like a cross between a 6V6 and a 6L6. As for the EL84, I know someone round here has had great luck with the adapters you can get, Tone Bones or something like that. Don't have any inside pics, sorry. Just noticed you mentioned the standby switch, you can safely hard wire it in the on/play position. There is no need for a standby switch on this amp, in fact it's affectionately called the 'self destruct switch' by many, as it can and w
  12. I tried a 5Y3GT and a pair of 6V6GTs a few years ago and had hum and a little red plating. I fixed the red plating by increasing the cathode resistor, but lost the amazing tone in doing so. If I didn't need to look after my 6V6s (I use them in my main amp) then I would try again and add bigger screen grid stoppers instead. Just an idea I thought would be worth mentioning! I think the hum might be coming from the 5Y3, you could try the 5Y3 with your 5881s to check that. Another thing, my FAVORITE mod is a pair of recessed side handles. Makes the amp so much easier to lift, especially wh
  13. For an effects loop you could try something like this. I haven't tried it yet but I'd expect it to reduce the level sent to the reverb tank a little, also the FX return is quite low impedance so line level FX modules will probably work better than typical stomp box type FX. I'd use shielded cable to link to the pot and sockets on the back of the amp. To increase return level and impedance you could probably use a 2k2 resistor instead of the 1k. -------------------------------------------------------------- Schematic above is updated to fix a bug in the FX return.
  14. This short article on amp design explains why standby switches are not necessary on guitar amps. P90's education is obviously focused on transmitter valves, a different beast entirely. Power Supplies and Standby
  15. Hi, I've just checked the schematics for your amps and neither of them will really benefit from the use of a standby switch. In fact leaving an amp in standby mode for too long is quite bad for the valves, google 'cathode poisoning'. NOS valves are often less susceptible to this due to purer cathode material, but if there is a chance you could forget that the amp is on then don't risk it. Several hours of standby will reduce the gain and lifespan of your valves. Standby switches are only useful if your amp has a DC coupled gain stage such as a cathode follower. Even then, there is a much b
×
×
  • Create New...