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Sorry! I didn't even think to record the changes. I will say that cutting the caps will reduce the brightness adequately to allow the use of the treble control on the amp's eq as well as the treble control on your instrument.


If you don't like the idea of cutting the caps you could simply desolder one or both legs of each of the caps and remove them from the circuit board. The only thing to consider here is that you would have to remove the circuit board from the amp's chassis to accomplish this.

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  • 2 weeks later...

Hi, I've read this thread through again. I've had my BC30 a few months now and have made a few mods.


Stock valves were EH 12AX7EH, Sovtek 6L6WXT+, Electron Tube 5AR4 (Chinese).


Replacement valves

V1, V2, Harma ECC83 Retro (Mullard rebuild)

V3, V5, (reverb) Stock EH so far

V4, (PI) Harma ECC83 Retro - balanced

V6, V7, NOS Philips JAN 6L6WGB/5881 (also tried Svetlana=C= 6L6GC)

V8, Sovtek 5AR4


Replacement speakers

Celestion Classic G12M-25 Greenback 8ohm

Celestion for H&K Rockdriver Pro G12-80 8ohm (something like a G12T-75)


The valves were replaced progressively, first the rectifier made a huge difference; the o/p made made a big change too, the Svetlanae were loud and clear but a bit sterile, so 6L6WGB/5881 it was; the retro ECC83 really are Mullard-like, nuff said, the EH fizzy toys.


The speakers, omg the speakers! The Celestions are louder, clearer and have more top and more bottom, more rock, and more roll, the business. I have added a switch to provide 16ohm or 4ohm the pair or individual 8ohm. The 16 ohm configuration is clearest and best, the 4ohm is muddy. I did this because (a) they are better speakers, (O:) I can now add my 2x12 ext cab in normal configuration.


Bright caps.

I lifted C6 and C5 (not C7) on the Ch2 Drive channel and

I lifted C3 and C4 on the Ch1 Clean channel.

I am not sure about that C4, I may put it back down.


I have seen no previous mention of lifting C4 - what views there?


Is there some reason for not lifting the C4 ?

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  • 4 weeks later...



I am about to embark on the CAP mod to try and cut some of the brightness of my BC30.

Having read and re-read this thread, I'm still a bit confused about the best way to approach this.


-Papa says do C6, then C5, then (if still unhappy) C10.


-Twanger is saying C3, C5 and C6 (but in no particular order).



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Earlier in the thread someone mentioned cutting the caps one at a time and then listening to the amp after each cap was cut. Since this may be a little new to you it might be a good procedure to follow. That way you're less likely to "snip a cap too far". If you do it this way I would follow papamidnite's order of making the cut(s).


Update on my BC 30 changes:

Papamidnite had mentioned THD Yellowjackets so I decided to find out what these were. They are a tube converter that let's you use EL84 tubes instead of the 6L6 power tubes. They drop the output of the amp to just over half. They also get overdriven easier. They do such a great job of getting overdriven earlier that I removed the Celestions and re-installed the Lady Lucks. This way I get more tube overdrive and less speaker break-up...a MUCH better sound! Not only that, the Lady Lucks have reached that point where they are fully broken in now and I'm really liking them.


Now I'm on to the reverb. Earlier I put a 12AT7 in the reverb drive to tame it. It tamed it alright but not enough for my tastes. I just put another 12AT7 on the reverb's output and it gave it a much smoother sound. Very mellow. The next thing to reign in is the long tail on the reverb. It's 3+ seconds long which is too long for me. There's also a "bump" in the reverb's sound that's just slightly louder than the original note. It wouldn't be so bad but there's this slight delay before the bump. If I made a simple graphic representation of it, it would look about like this: ___--________


So I'm kicking around a couple of ideas. First is the reverb transformer. Next is perhaps one of the caps from c20 to c23 should be changed as one or more of these may be the culprit adding in the delay before the bump. Maybe replacing r25 with a pot may work. I'm going to look at some other amps schematics to compare reverb circuits and see if I can come up with a solution or at least a working idea.


Other than that I'm extremely happy with the BC 30. It sounds great.

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Guys...thanks x 100!!!

Just snipped the C5 and C6 caps (one at a time with sound test in between) and WOW!!!

The difference is tremendous.

Had previously swapped ou the rectifier and power tubes for mesa 5ax4 and 6L6s respctively, changed the V1 and V2 to Marshall branded Ecc83s...but this mod has sweetened it up even more.

Thanks for the thread and the useful tips and support.

Rock on!!!


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  • 4 months later...

My improvement looks like:


- R3, R15, R21 are 1K5 resistors - These are the factory values!

- R8 is 10K resistor (!) - It is a factory value!

- C3, C10 cut

- C5 is jumper wire - yes that is a direct connection to the first two degrees of amplifications


Tubes are Ei ECC83 for V1-V5, output tubes are Tungsol 5881 Platinum matched (from Banzai).


The tone is now very warm and sweet, drive channel has a depth and sufficient strength.

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Like others have done I snipped C3, C5 and C6. At first I liked it but later realised something was missing, you lose treble but you lose dimension too. I fitted a triple pole mini toggle switch and wired the capacitors through the switch so I can switch em back into circuit whenever I need. It's like a bright switch.


I also replaced R3, R8, R15 and R21 with 1K/1 watt resistors. The GZ34 rectifier is now gone and replaced with a solid state recifier, this however has raised the plate voltage to 450 VDC.


I wanted to fit EL34's so I replaced R45 and R46 with 1K/5 watt resistors, popped in a pair of EL34's and it worked fine however with 60mA of cathode current at zero signal I replaced the shared cathode resistor R44 with a 330 ohm 25 watt alternative which is now mounted if front of the fan for better cooling. Cathode current is now 50mA per tube and this amp is running like a dream. The fizz I had with the 6L6 tubes is gone, now I have creamy overdrives and gorgeous cleans.


I use a THD hotplate attenuator so channel 1 cranked up gives the best overdrive tone of all. This amp is superb now. I might yet fit another input jack socket and maybe look into building a tremelo circuit and effects loop. But they are considerations for the future and not exactly easy mods to perform.

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  • 2 weeks later...

An update, I posted some mods some months ago on this thread -


Well the speakers are now a pair of Celestion Classic G12M-25 Greenbacks.


Regarding the schematic, the Ver001 is out of date, many of the mods indicated here were already made to my BC30 bought in spring 2009.

R3 is 1.5k not 2.2k; C3 is 101 not 471; C5 is 471 not 101; R8 is 1.5k not 2.2k; R15 is 10k not 2.2k;R21 is 1.5k not 2.2k; R23 is 5.6k not 10k; VR7 is 250k not A1M; VR5 is B250k not A1M. There may be others.


I have measured A=418V B=417V C=338V D=206V E=286V Cathodes = 34.3V. Pin4=415V triode, 416V pentode. (NOS Philips JAN 6L6WGB)

I note that there is an unused PT1 60VAC tap in the mains transformer for grid-biasing a la Bassman.

I tried putting different caps e.g. 22uF across R15 and got a very extreme drive sound, it was too much for me, removed again.

re the valve order V1a is common preamp, V1b and V2a are the drive 'channel', V2b drives the tone control, V4 is the PI, V3 and V5 are the reverb, V6 and V7 are the OP, V8 is the rectifier.


I have put a DPDT bright switch on C4 and C5, it does both at once. But now C3=471 C4=101 C5=471 C6=101


That */confounded standby switch packed up! Twice I replaced it. Nasty crackling at high volume and then volume loss. Eventually the back of the switch sprang out (bad HT can blow fuses too). The 5AR4 has a slow start and needs no standby. I've removed it and replaced R39 with a B250k Master Volume knob. Now that tames this beast. I had gigged it in 15 watt triode mode and had been asked to turn down so we could hear the the Marshall half-stack! I think the cab is very directional, if you stand over it you cannot hear it so well and it needs tilting back to throw its voice up. Now with the Master Volume added I can use it at home until the wee hours, and it still winds up to '12'.


I have made some mods to the tone stack but am not entirely happy with them. Altered C16 R22 C17 R23.


Has anyone else made mods to the tone stack, what did you do?

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Here's an interesting bit...compare the following schematics....

BC30 - http://www.ppwatt.com/files/ppwatt/EPIPHONE_BLUES_CUSTOM_30_SCHEMATIC_VER01_DPPT.pdf

SoCal 50 - http://i28.tinypic.com/19ms0p.jpg


Other than transformers and output power tubes I don't see much difference.


Thanks for those links.


The transformers appear to be the same. My BC30 may be getting grid-biased. The mod is very simple. Most of the wiring is already in place. Would -45V be about right ?


Unfortunately the wiring is messy and I think it is contributing to the loud hum, I shall have to tidy it up. I do not like seeing the HT and mains circuits on the main PCB, rather stuck with that but the festoon of cables is all wrong.


Do you get mains hum ? Have you cured it ?

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My improvement looks like:



- C5 is jumper wire - yes that is a direct connection to the first two degrees of amplifications



What does C5 jumper to?


I've been holding out on modding my BC30 which is 2005 model, and now that it's clear there are differences in the older and newer models I'm a little confused as to what to do. It might be a mistake to incorporate 2009 specs to a 2005 model without going over both schematics closely.

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My improvement looks like:


- R3' date=' R15, R21 are 1K5 resistors - These are the factory values!

- R8 is 10K resistor (!) - It is a factory value!

- C3, C10 cut

- C5 is jumper wire - yes that is a direct connection to the first two degrees of amplifications


Tubes are Ei ECC83 for V1-V5, output tubes are Tungsol 5881 Platinum matched (from Banzai).


The tone is now very warm and sweet, drive channel has a depth and sufficient strength.[/quote']


In my BC30, R3 R8 and R21 are 1k5, and R15 is 10k. It is a recent amp bought early this year. The 'ver01' schematic shows other values (all being 2k2), those are the values fitted to it, I did not change them. However I have fitted a 4k7 jumper to R8 dropping the value to 3k2. Fitting a 2 to 22uF cap across R8 results in a lot of drive, too much for me.


Is a later schematic available?

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Update - Tone Stack - today I changed R23 to 10k (it was 5.6k fitted) tone is now much smoother and sweeter whereas before it had a harsh edge to it. I have experimented with various component but now it is more-or-less to the 'ver01' schematic with the exception of the pots which are 250k - as fitted - i.e.



R24=100k this also gives a better balance between interactive/independent modes.





VR5, VR6, VR7 = 250k


The aggressive snarl is still there if wanted, just tweak the tone pots, but before I could not get rid of it, it was present throughout the entire range. Now I can go from jazz to metal. And with the master vol go from late-night practice to, well you know how loud these BC30 are.

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Well today we had a spot of bother, The BC30 started making spitty crackling noises on Ch2 when at loud volume, but only on a few notes around middle-C. Weird.


Solutions tried :-

Swap bottles V1 and V2 - do dice.

Replace EH bottles V3 and V4 with Mullard ECC81 (12AT7) and Harma ECC83-STR- no dice, in fact the reverb went very quiet, I assume the poor old Mullard does not have enough gain left in it ;-( - used a pair of Harma E83CC - now the reverb's back but still no dice with the snot, crack and spottles.

Started poking the solder on the valve bases, assume they used lead-free (nasty stuff), Sure enough, spap crackle and pop on three bottles. Lead-free or just plain old bad workmanship and the joint de-wets and you get a dry joint with intermittent or high resistance. Re-soldered the valve bases with pukka tin-lead multi-core. Also re-seated the op bottles and rectifier. - sorted. But- OMG! The Volume's Back! I didn't notice it go but now it's like four times as loud as it was this morning - Ouch! - and a good job I fitted that master vol. Happy bunny now.


These amps are a good design, they sound good when they're working and have mostly good components but I've had several problems with the build quality now.


Today's lesson = check the solder joints on the PCB.

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Howdy, new to this forum... Got a BC30 a few days ago, like it a lot. However, would like to get a more 'open' sound. I would say I hear it 'compressed'.

Haven't bought any replacement tubes yet but am planning on getting a few tungsols 12ax7, maybe some gt 12at7 or 5751 to expetiment with PI and reverb and a couple of 'soft' tungsols 5881...

I want the most headroom I can get on this amp and would like to get more on the touch sensible territory. Was wondering if the mods described here will help me or are you guys normally playing with breakup?

Thanks for all the info already posted!

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Update here' date=' clipped c5 and pretty much obtained what I wanted. (thanx!)

Only thing that I'm not satisfied with now is the reverb section... If anyone comes up with a way to tame it do tell.[/quote']


er, buy a Laney? ;-)


Me, I quite like the reverb, but then I want more...


1) turn it down


2) change reverb driver bottle V3 - I tried a Mullard ECC81 in there, more current, less gain (but 12AT7 may suit you). I did not like it so I tried another make ECC83, still not enough gain and 'thinner' sound, so went back to stock EH 12AX7. Swap bottles V3 and V5 until you find ones you like.


3) the tank may be loose and microphonic (driven by the speakers), make sure it is secured to the floor and in its bag. There are things you can do to tanks to make them more or less flabby.


imo changing the 5AR4 rectifier made a big difference to the openness of sound.



Changing the subject, there is an AB165 to AA864 (silver to black face) mod that swaps what would be C25 and C26 in the BC30 from 22nF for 100nF. The ver01 schematic shows these as 22nF but they are already 100nF fitted in mine.

Does the So-Cal50 also have so many changes from the drawing?

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  • 3 weeks later...

+1 Castors, I fitted some.


Also note that the amp must be tilted back when playing with a band other wise to the sound flaps around the player's legs and he will have the amp set to drown everyone-else.


to summarize my mods, and they are actually very simple -

bright caps C3 and C5 lift or remove

bright caps C4 and C6 lift or remove, or fit DPDT bright switch. Note correct value 101 = 100pF

V2A cathode resistor R15 is 10k, gain is too great (lack of cap here means some negative feedback) shunt with 4k7 to make 3k2

N.B. tone stack C16 is 471 = 470pF, increase to about 680pF (I put 3 x 220pF in parallel). And I'm pretty sure I've put R23 back to 5k6 from the 10k I fitted

N.B. Master Volume - replace R39 with linear B250k on shielded cable run (it went in hole left by standby switch)


Other stuff

I bypassed and replaced the standby switch

N.B. I fitted a pair of Celestion Classic G12M-25 Greenback 8 ohm (series into the 16 ohm outlet). Warm tones.

I've replaced all except the reverb bottles with better stuff (see earlier/other posts/elsewhere/TDPRI)


The stock BC30 is considered very harsh and biting, by many. With these mods, this amps get compliments on how smooth and rich it is. Now it can go from warm smoky jazz, through heavily over-driven blues, to bitingly clean telecaster twang.

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