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Old November 17th, 2009, 03:48 AM   #1 (permalink)
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epiphone blues custom 30 tube schemo

I just became a member and all of the old links to the schematics on the epiphone BC 30 have led me to dead ends. Any help would be appreciated as I want to finish re-tubing this bear and snip some of those high end caps. It's an amazing amp for the $$$ but does need some tweeking. I changed the rectifier tube and what a difference!!! just got some new power tubes, next I want to replace the 12ax7's, PI, and reverb tubes, but need to know a bit more as I am new to doing my own amp repairs/upkeep!! any help (links) appreciated greatly by this newbee.....THANX

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Old November 18th, 2009, 08:25 AM   #2 (permalink)
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Originally Posted by bad kat punk LP View Post
I just became a member and all of the old links to the schematics on the epiphone BC 30 have led me to dead ends. Any help would be appreciated as I want to finish re-tubing this bear and snip some of those high end caps. It's an amazing amp for the $$$ but does need some tweeking. I changed the rectifier tube and what a difference!!! just got some new power tubes, next I want to replace the 12ax7's, PI, and reverb tubes, but need to know a bit more as I am new to doing my own amp repairs/upkeep!! any help (links) appreciated greatly by this newbee.....THANX
Hey man;
I've been down a similar research path with the BC30. If you haven't been there already the amp section in the Epiphone forum has quite a bit of stuff -
http://forums.epiphone.com/default.aspx?g=topics&f=4
There is a thread there (http://forums.epiphone.com/default.aspx?g=posts&t=6812) - that and has plenty of stuff about what caps to snip. I have a copy of the schematic and can email to you if you like. But I think you can download it from a post on this page (look for jefrs quotation of twanger's post):
http://forums.epiphone.com/default.a...sts&t=6812&p=5

I've thus far worked with the stock amp and just fiddled with tubes. I found the stock Sovtek rectifier tube in mine to sound, or feel, better than a JJ replacement I purchased. Changing the preamp tubes has a big effect on tone - mine came stock with Chinese 12ax7bs - replaced them with EHX 12ax7ehs. Certainly an improvement. Putting lower gain tubes in the PI position reduces the output a bit and gives a lower gain sound. Putting lower gain tubes in the reverb send and return (v3 and v5) positions reduces the reverb's intensity quite a lot - I like the 12ax7 sound best; but I'm into reverb and echo etc.

I have Sovtek 6L6wxt+ power tubes which sound pretty good after a burn in period. My amp was an older one and came with Sovtek 5881s and they were pretty brittle and flabby sounding - although I don't mind these tubes in the right amp. I have some Svetlana 6L6gc tubes on the way. You can put KT66s in these amps too - I have contacted Gibson and they have assured me the amp's output tranny can handle it. In fact you can actually put any member of the 6L6 family into these amps - with yellow jackets you can also put in EL84s.

It is a good amp but takes some time to dial in. I'm not keen on snipping caps myself. I usually just play through the dirt channel (gain between 1 and 3 'o' clock) because the clean channel doesn't take dirt boxes that well IMO. I also run it on 30 watts as mine hums in 15 watt mode. I use independent eq mode and keep the mids down pretty low (like 8-9 'o'clock), as thats where all the icepick sound is. In addition, I jack the bass right up and run the treble between. But I do run the mid on the dirt channel on full. I can get a pretty good sound this way that's not too bright. Sort of sits midway between a Vox and Fender sort of sound. Oh yeah - from all the things I've read you shouldn't use the standby switches on these amps - it can ruin the rectifier tube. As a guy at the Epi forums said:
"because we have a 5AR4 rectifier in the BC30, we don't need no standby switch, the 5AR4 has a slow warm-up by design, to allow the heaters to get up before the HT (there's a problem called 'cathode poisoning' or 'sleeping sickness' caused by using standby switches - see article 'standby for the truth' by Hartley Peavey)."

Last edited by wildschwein; November 18th, 2009 at 09:20 AM.
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Old November 19th, 2009, 09:07 PM   #3 (permalink)
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From memory and my schematic...
I have changed all the valves except those on the reverb for Harma Retro ECC83 (Mullard rebuilds). The 5AR4 is now Sovtek. I have used NOS Philips JAN 6L6WGB, (the Sovtek 6L6WXT+ weren't bad though), also JJ 6V6GTS (the HT is a little too high for other 6V6 and old NOS 5881), but the current op valves are Svetlana =C= 6L6GC. I have not tried EL34 nor KT88 although the board is wired for pentodes and they do fit the SoCal50. The Philips 6L6WGB (=5881) and the JJ 6V6GTS sound similar, the 6L6GC are a little more open.
The speakers are Celestion Classic G12M-25 Greenback, but they are 8ohm each wired in series or parallel with a DPDT switch, I normally use them at 16ohm. I do have a Heritage G12H-30 in my Laney L5T, it is a better speaker but gets confused with the different Classic G12H-30.

The schematic I got from Epiphone Europe is incorrect, apparently it is for an earlier version. I have fitted a single bright switch DPDT to both clean and drive which lifts C4 and C6 but they are 101 (100pF), C3 and C5 are permanently lifted. R3 and R8 are 1k5 as fitted. R15 is fitted with a 4k7 shunt across the fitted 10k to drop it to 3k2. In the tone stack I replace C16 with a 220pF, then added two more in parallel i.e. 660pF there. the tone pots are VR5=B250k (not A1M), VR7=A250k (not A1M), VR6= A250k, as fitted, R22=47k, C17=100nF, C18=22nF, (no changes) but R23 is 5.6k as fitted (not 10k as shown).

The standby switch destroyed itself so I bypassed the connections, there is no need of a standby with a 5AR4. The hole I filled with a square washer and a B250k Master Volume pot replacing R39 (on some shielded cable).

That's it really. Lift C3 and C5. Bright switch (or lift) C4 and C6 but put them back to schematic values of 100pF. Tone stack put a 220pF across the 470pF C16 to make 690pF. Replace R39 with a B250k Master volume. Replace the speakers. Replace the 5AR4 with a Sovtek and the 12AX7 with your bottles of choice. Putting bigger op valves in won't give you more watts (it's the HT and bias) but will change the tone.

I was the guy on the Epi forum... but then my standby switch was arcing and did destroy itself.
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Old November 20th, 2009, 12:05 PM   #4 (permalink)
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I was the guy on the Epi forum... but then my standby switch was arcing and did destroy itself.
Sorry jefrs - I should have checked to see if you were over here too. Thanks for all the BC30 info though both here and over at the Epi forum.
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Old November 20th, 2009, 09:21 PM   #5 (permalink)
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Sorry jefrs - I should have checked to see if you were over here too. Thanks for all the BC30 info though both here and over at the Epi forum.
No worries mate.
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Old November 21st, 2009, 11:10 AM   #6 (permalink)
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my mods + schematic here http://www.tdpri.com/forum/amp-centr...ml#post2146521
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Old November 22nd, 2009, 12:12 PM   #7 (permalink)
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Wow, being new to this forum, I want to thank everyone who responded to my questions about the BC30. I really appreciate all the help. you guys are ACES!!!!!!
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Old November 27th, 2009, 08:41 AM   #8 (permalink)
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I just dropped the Svetlana 6L6GCs into my BC30 - man, these are awesome tubes and not that expensive. I picked up a new pair for about $35US on eBay including postage. It's totally rounded out the sound of the amp. Incredibly rich piano-like sounds on both the dirt and the clean channels. This is how a valve amp should sound.

With the stock Sovtek 5881s and the later 6L6WXTs I put in the amp sounded very flabby on the bottoms and fizzy on the tops, it also didn't seem that loud. The Svetlanas in comparison just sound huge, even in 15 watt mode, where I still have a minor hum, the amp is freakin' loud. The bottom end is monstrous but doesn't fart out. The tops are refined and far less brittle. Mids are almost EL34-ish/Marshally. I don't think I've heard as good a sounding new power tube as this one. The tubes I purchased look like this:

I guess this is probably the Reflektor-made version rather than the winged c but it sounds great in the BC30. The native bear trap retainers won't grab the base of these tubes though; but they are a tight fit anyway. Maybe spring retainers might be in order at some point.

I also changed out the Sovtek Rectifier tube for a JJ and it gets along well with these power tubes. I left my reverb tubes (V3 and V5) as stock 12ax7b Chinese tubes and the other three bottles are EHX 12ax7EHs. I think I've found a formula that works - this amp is now inspiring to play.

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Old November 27th, 2009, 09:31 AM   #9 (permalink)
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I'm interested in this amp and have read all the posts on the epi forums, but I'm worried it's just too much of an amp physically; I would very much appreciate it if someone could be so kind to post the dimensions. The manual is impossible to find online and while I found enough references to the weight I can't seem to find anything related to size.
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Old November 27th, 2009, 10:33 AM   #10 (permalink)
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In metric it's approximately 65cm x 50cm x 27cm.

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Old November 27th, 2009, 11:32 AM   #11 (permalink)
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Thanks very much! Too wide unfortunately
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Old November 27th, 2009, 01:58 PM   #12 (permalink)
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Well, it's a 2x12, all 2x12 combos are about that size and equally as heavy.

The manual is a leaflet that contains nothing of great interest.
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Old November 27th, 2009, 02:45 PM   #13 (permalink)
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Well, that's true of course. It just seems such a cool deal for the money and I guess I was looking for some justification ("look honey, it's cheap and not that big") to squeeze in another amp.
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Old November 27th, 2009, 09:44 PM   #14 (permalink)
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Well; I'd say it's probably smaller than a Fender Twin.
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Old November 29th, 2009, 08:09 PM   #15 (permalink)
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New Big bottles in my BC-30

Quote:
Originally Posted by wildschwein View Post
I just dropped the Svetlana 6L6GCs into my BC30 - man, these are awesome tubes and not that expensive. I picked up a new pair for about $35US on eBay including postage. It's totally rounded out the sound of the amp. Incredibly rich piano-like sounds on both the dirt and the clean channels. This is how a valve amp should sound.

With the stock Sovtek 5881s and the later 6L6WXTs I put in the amp sounded very flabby on the bottoms and fizzy on the tops, it also didn't seem that loud. The Svetlanas in comparison just sound huge, even in 15 watt mode, where I still have a minor hum, the amp is freakin' loud. The bottom end is monstrous but doesn't fart out. The tops are refined and far less brittle. Mids are almost EL34-ish/Marshally. I don't think I've heard as good a sounding new power tube as this one. The tubes I purchased look like this:

I guess this is probably the Reflektor-made version rather than the winged c but it sounds great in the BC30. The native bear trap retainers won't grab the base of these tubes though; but they are a tight fit anyway. Maybe spring retainers might be in order at some point.

I also changed out the Sovtek Rectifier tube for a JJ and it gets along well with these power tubes. I left my reverb tubes (V3 and V5) as stock 12ax7b Chinese tubes and the other three bottles are EHX 12ax7EHs. I think I've found a formula that works - this amp is now inspiring to play.
I also changed the rectifier tube and put two larger Ruby 6L6GC tubes in my BC30. Man, what a difference!!!! I am interested in changing out the rest of the 12ax7's but am not too sure which 2 are the reverb tubes yet. Either way, so far so good. I think I'm going to change one of the speakers with a greenback (25watt) or a clone....this amp is steadily becoming better and better with minimal upgrades!!!!!
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Old November 29th, 2009, 09:46 PM   #16 (permalink)
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Well; I'd say it's probably smaller than a Fender Twin.
Fender Twin Reverb (RI) = 20x26.5x10.5-in 64-lb
Epi BC30 = 21x26.6x10.9-in 70-lb.

So the beastly-30 wins the hernia stakes.
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Old November 29th, 2009, 09:54 PM   #17 (permalink)
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The reverb and other valves are shown in the schematic posted above.

If memory serves, the reverb pair are the two either side of the white reverb phono socket. I mark chassis with an inedible marker showing the number and alignment.

The little bottles run in a staggered line V1, V2, V3, V4, V5. The big bottles are in line above V6, V7 and V8 - the rectifier.
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Old November 30th, 2009, 10:42 PM   #18 (permalink)
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The reverb and other valves are shown in the schematic posted above.

If memory serves, the reverb pair are the two either side of the white reverb phono socket. I mark chassis with an inedible marker showing the number and alignment.

The little bottles run in a staggered line V1, V2, V3, V4, V5. The big bottles are in line above V6, V7 and V8 - the rectifier.
Thanks for helping out....being new to "working" on my own amp, I don't fully understand the schematic completely. Is there anything particular I need to know about picking out 12ax7 tubes. I understand about using matched pairs with the output tubes but I don't know if there is anything I need to know when choosing 12ax7;s or ECC83 tubes for the pre-amp tubes, the phase inverter, and the reverb tubes???? any help appreciated!! Thanx
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Old December 1st, 2009, 08:24 AM   #19 (permalink)
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Across the top of my schematic are V1, V2, V4. Either side of [REVERB] are V3 and V5. Below are the output pair V6 and V7. Below is the rectifier V8. Sorry my schematic is blurry, I had to reduce it to upload. Ask Epiphone support for proper one.

A 12AX7 is an ECC83.

You can drive yourself mad choosing 12AX7/ECC83 variations, there are so many different ones. Avoid cheap and nasty wasp in a jam jar types. Avoid expensive unobtanium types, avoid cryo added bs types.

A 'balanced' ECC83 for the V4 phase inverter - both sides of the bottle are matched by selection, they are supposed to be built that way, but...

The reverb valves V3 and V5 need nothing at all special. Mine preferred the stock EH to Mullard, go figure. Try 'high gain' types.

The input valve should be silent and of high quality and the drive valve can be high gain, but the BC30 uses V1 for both input/clean and drive, and V2 for drive and tone. So just use good standard bottles.

It is nice but not entirely essential to use 'matched' output pairs but they must be a pair, not mixed makes and numbers.

The BC30 is built for 'modern' 5881. You can use any bottle rated for more than 420VDC. That rules out old school 5881, 6V6 and 6L6(A) but does allow Soviet/military 5881(=6L6WGB), 6L6WXT+, 6L6GC, EL34, KT88 and the JJ-6V6GTS. The 5881, 6L6GC and the JJ-6V6GTS types are sufficiently similar to not need re-biasing because it's cathode/self biased (you won't get more power from the bigger bottles unless you do re-bias). I considered going to fixed bias on this amp but I really do not need it to be any louder. Different type valves give different gain curves and so a different sound to the amp, me, I chose the bottles for sound quality.
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Old December 1st, 2009, 09:29 AM   #20 (permalink)
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You can use any bottle rated for more than 420VDC. That rules out old school 5881, 6V6 and 6L6(A) but does allow Soviet/military 5881(=6L6WGB), 6L6WXT+, 6L6GC, EL34, KT88 and the JJ-6V6GTS.
So, can you just drop el34s or kt88s into these without any component mods? I think I'd try it if I knew it wasn't going to fry anything. I know kt66s are no problem - a Gibson sales rep assured me they were plug and play.
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