jefrs
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Posts posted by jefrs
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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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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.
R22=47k
R23=10k
R24=100k this also gives a better balance between interactive/independent modes.
C16=471
C17=104
C18=223
C19=472
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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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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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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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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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, (
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 ?
I can now add my 2x12 ext cab in normal configuration.
Blues Custom Mods
in Epiphone Amps & Accessories
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A question
If the Beastly30 is designed by Pyotr Belov and the So-Cal50 by Mike Soldano, how come they're identical circuits (barring op valves and rectifier) ?
Confused...