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chrisbagi

Blues Custom 30 preamp slots.

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Hi all,

 

I am new here and this is my first post and was wondering if you guys can help me out on identifying the pre amp slots on BC30 I would like to experiment with tubes, but also want to know what tube slots control or change tones and sounds. I am looking to change my gain and the reverb in the amp. So in other words I would like to know what is V1, V2, V3, V4, V5, what it controls in the Blues Custom 30. I hope this makes a some sense.

 

Thanks.

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V1 = CH1 preamp

V2 = CH2 preamp (fed from CH1 preamp)

V3 = Reverb in

V4 = Phase Inverter (PI)

V5 = Reverb out

 

The Czech made JJ tubes (also sold as Tesla, Ruby and perhaps others) are good preamp tubes in the V1, V2 positions. A higher gain tube like the SovTek or Groove Tubes would be good in the V2 position.

 

To mellow or sweeten the reverb it would be good to use a lower gain 12AT7 or 12AU7 in the V3, V5 positions.

 

For the V4 PI position I would highly recommend a Groove Tubes MPI (Matched Phase Inverter) 12AT7 since their tubes are tested to find which ones are closely balanced in output. It's only a couple of dollars more than a "standard" tube and worth every penny.

 

For helpful info on the BC30 you might also want to check out this thread:

http://forums.epiphone.com/default.aspx?g=posts&t=6812

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You're welcome. I've gained a lot of helpful info here and am glad I can give some back.

 

Here's a link to the BC30 schematic. It's in *.pdf and has been very helpful:

http://www.ppwatt.com/files/ppwatt/EPIPHONE_BLUES_CUSTOM_30_SCHEMATIC_VER01_DPPT.pdf

 

Also, on the circuit board in the BC30 all of the components are numbered on the circuit board as they are numbered on the schematic so they are easy to identify.

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Yea I got the Schematic, thats cool. One question on the V4 slot what does this phase inverter do, does this help out on the EQ? I will pick up a (Matched Phase Inverter) 12AT7 if it sweetens the sounds even more.

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That's kind of tricky. If you are familiar with audio signals or any kind of wave you know that there is a zero or reference line. Above this line is the high or + part of the signal or wave. Below this line is the low or - part of the signal or wave. I won't go into all of the technical details here but when the signal from your guitar enters the amplifier it basically gets split into +/- and each half of the signal gets processed through the circuitry. In the case of an amplifier that processing = amplification. This processing flips the signal around. Sort of like an image you see through a lens is upside down. The phase inverter corrects this upside down signal before it enters the power tubes. Assuming (this is dangerous, I know) that the rest of the signal path is correct through the transformer and on through the transducers (speakers) the sound from your guitar will be produced by the speakers correctly the way the sound entered the amplifier. This means that the speaker cone will move forward with every positive input from your guitar. This is what helps us all hear and work with the dynamics of our instruments.

 

If I may go philosophical here for a moment...those of us who play electric or electronic instruments are not just playing our chosen instruments. Neither are we just playing our amps. When your instrument is plugged into it's signal chain which includes the amp and speakers we are now playing a system. In other words, the end of our instrument is the speaker(s). The whole thing is our instrument. This is why amp selection is every bit as important as the selection of one's guitar or bass or fiddle or keyboard. It forms the basic signal chain which is your instrument. Other things that you insert into that chain like processors and stomp boxes also become part of your instrument. The whole is your sound.

 

You made a good selection with the BC30. This amplifier has lots of potential. It sounds decent out of the box and with a few minor changes it puts out some excellent tones and makes for a great basic sound.

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Thanks twanger, and now I will start doing some research on pre amp tubes and head down to the music shop ask info down there, I have a buddie that loves to swap tubes every so often.

 

Cheers.

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The way I read the schematic

V1A = Common to Ch1 and Ch2 (first input valve)

V1B = Ch2

V2A = Ch2

V2B = Common to Ch1 and Ch2 (before t/c)

V3A+V3B (in parallel) = Reverb Send

V4A+V4B (in parallel) = Reverb Return

V5A+V5B = Phase Inverter

V6, V7 = output valves

V8 = rectifier

 

V1 and V2 are half-and-half.

The V1, V2 is odd in that half of V1 is the clean/common Ch1 and half of it is the drive Ch2

and half of the V2 is the drive Ch2 and half of it is common to both channels before the tone controls.

For some reason it is 'normal' to use the B-section as the primary so V1B should be the first then V2B, V2A and V1A, but we're stuck with the way it is.

 

This makes it tricky to stick a clean valve in the clean slot and a dirty valve in the drive slot.

 

I put some 'retro' Mullard remakes in mine, with a balanced PI, much better than the fizzy EH stock. The biggest improvement was to replace the Chinese 5AR4 rectifier. The reverb valves could be 12AT7/ECC81, as could the PI, I have not tried that (yet).

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V1 = CH1 preamp

V2 = CH2 preamp (fed from CH1 preamp)

V3 = Reverb in

V4 = Phase Inverter (PI)

V5 = Reverb out

 

The Czech made JJ tubes (also sold as Tesla' date=' Ruby and perhaps others) are good preamp tubes in the V1, V2 positions. A higher gain tube like the SovTek or Groove Tubes would be good in the V2 position.

 

To mellow or sweeten the reverb it would be good to use a lower gain 12AT7 or 12AU7 in the V3, V5 positions.

 

For the V4 PI position I would highly recommend a Groove Tubes MPI (Matched Phase Inverter) 12AT7 since their tubes are tested to find which ones are closely balanced in output. It's only a couple of dollars more than a "standard" tube and worth every penny.

 

For helpful info on the BC30 you might also want to check out this thread:

http://forums.epiphone.com/default.aspx?g=posts&t=6812[/quote']

 

Sorry for my ignorance, but when i open the back and I'm looking at the 12ax7 slots, do i read positions 1 - 5 as starting from the left and moving right?

thanks.

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Eeeee...I don't remember. I do remember #5 is closest to the transformer. I can't get to the amp at the moment to look but I'll double check.

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I have the So Cal 50 by the same designer and uses the same chasis & tube layout as the BC30 only flipped upside down and w/o a rectifier tube. Also it has a Presence control and the Drive/Gain channel has a 'Contour' control instead of a 'Mid' knob.

Anyway, I determined on that amp that V1 & V2 are channels clean & dirty respectfully.

I thought V3 was for the EQ section but maybe it's the 'reverb in' as this thread for the BC30 is saying.

The 'reverb in' line is near V3 tube but the 'reverb out' line is nearer V5 on the So Cal.

I found (or think) that V4 is actually the PI slot and V5 was the 'reverb send/out'.

 

I tried and currently use a 12AU7 in V5 slot which tamed the reverb so I'm sure V5 is a 'reverb out' on the So Cal.

Also, I tried the V5 with the 12AU7 with desired results before I put a 12AT7 in the V4 "PI" slot so thats why I think I'm correct. In fact I've been rolling a 12AX7 &12AT7 in the V4 slot with no differances in reverb response/volume, another sign I think I'm correct.

Usually the PI slot is the last tube nearest the transformer or Output tubes, as in the BC30, but not always. So far I've primarily used my ears but I also think I found the ties to the output tubes from V4 indicating it is the PI tube on the So Cal schematic, but I am a layman and may not have read it right, you know, the dislexia and all, LOL

 

So am I wrong now about V3, is it a 'reverb in' or does it function as EQ (the Countour control?) as I, maybe falsley, presumed?

 

Here is a link I found to the So Cal schematic, http://i28.tinypic.com/19ms0p.jpg not as great detail as the BC30 posted previously (you can click the image to make it somewhat larger) but maybe enough for one of you to determine better than I could.

I know this is a Blues Custom thread but since they are practically sister/brother amps I thought I'd "butt" in!!!

 

peace & tone,

JoS

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thanks...still trying to determine which position is which.

Also' date=' does anyone know where i can get a PDF of the owner's manual on line?

[/quote']

 

Looking at the amp from the rear as it is mounted in the cabinet the #5 position is the one on the left next to the white reverb connector. You can count backwards from there as the tubes are lined up numerically.

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Thanks Twang' date=' you ROCK!!!

 

JoS[/quote']

 

You're welcome!

 

Just want to avoid confusion... my handle is twangER. There's a gentleman here who posts under the handle of TWANG. When I signed up my first choice for a handle was already taken so I was instantly struck with the "deer in the headlights" syndrome. I immediately thought "twanger", put it in and it was accepted. It was after that I came upon a post by TWANG and I knew confusion would come around someday.

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Looking at the amp from the rear as it is mounted in the cabinet the #5 position is the one on the left next to the white reverb connector. You can count backwards from there as the tubes are lined up numerically.

 

 

 

And on the So Cal it is the opposite, looking at the amp from the rear, V1 is on the far left nearest the input jack.

But since this is a head and you can access the tubes from the front then V5 is farthest left and V1 is far right nearest the jack. Which again makes sense as it is the BC 30 chasis flipped over. So it's just as easy to say that V1 on both these amps is nearest the input jack and count forward/backword from there.

 

And now that I know V3 is the reverb input tube then I'll probably experiment and try the 12AU7 I now have in V5 there. Great, more tube rolling, just can't leave it alone, LOL!!!

I may also put the V4 12AT7 in there and a balanced 12AX7 back in the PI slot although I seem to prefer the 12AT7 I have there now, it seems to make the amp a little more "alive", kinda subtle though. Also there doesn't seem to be much increase in gain on the gain channel between the 12AT7 and the 12AX7 in the PI slot of this amp although the clean channel seems to get atad 'edgier' eariler at the same volume setting than with the 12AT7.

 

So thanks again Twanger and sorry for any confusion, I was just using 'Twang' as short for Twanger. I will make sure my lazy butt types the 2 extra letters next time, LOL!!! Seriously, thanks again and too everyone on this forum, it's always a pleasure to read posts from kewl reasonable people that are informative and fun, I've really learned quite alot from here!!!

 

peace & tone,

JoS

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