Members Yan M Posted February 4, 2015 Members Share Posted February 4, 2015 Yes,you're absolutely right,I didn't take the time to re-wire and route cause I wanted to keep the stock circuit(warranty reasons)but your post makes me feeling like going further.One can unsolder the B&W wires right where they start on the PCB("Fil")and replace them with someting more serious:if properly done,it could be reversible should we (unlikely)have to return the amp.Thanks for the pictures!I will post more tomorrow as promised Link to comment Share on other sites More sharing options...
Members Yan M Posted February 5, 2015 Members Share Posted February 5, 2015 here are the pictures,one can see the 2W 100R resistor on the B&W fil supply ends.Some put a 2W 100R(not 100K!)pot with the two opposite lugs on each B&W ends,wiper grounded,then they try the best setting.The other pictures show the bias setting and fil separate tranny(there's something I must check with it,just pretty difficult to take apart)One can see as well the fil wires starting point on PCB. Link to comment Share on other sites More sharing options...
Members crsnot Posted February 5, 2015 Members Share Posted February 5, 2015 Thanks Yan , that looks pretty simple to me. I am going to try rewiring the heaters as per the recommended way this weekend and see what that does to the hum and then I will add the resistor to see if it further dampens the hum. I'll come back with photos and wether it works or not.I have read so many reports that the amp sounds good but the hum was too much and the amp was returned with no fix. I would have thought that someone would have come up with a solution . Maybe because only 3000 were made?You seem to be fairly technical.....any idea on how I can change the input arrangement to give a higher resistance? Most amps are 1M input but this one only is 500k. To change most amps to higher resistance input it is just 1 resistor ( a 1M "grid leak" resistor) changed to the required value. This change can dull the amp down a little but it doesn't cut the lows for a crystal harmonica mic which is what I want it for.I'd like to cut highs even more than the dark input does also but that can be further down the mod trail!Scotty Link to comment Share on other sites More sharing options...
Members Yan M Posted February 6, 2015 Members Share Posted February 6, 2015 Strange things occurs in designing,not always for the best...seen so many(good) products sunk by a 10cent forgetting.Engineers moves in mysterious ways...Fortunately,tube amps technology beneficiate from a(very!) long experience of enthousiasts: trial&error, tinkering,etc..As you said,the best option is to first rewire to best standards,then try the resistance trick.This "fixing" is harmless anyway...and costless too.As for your input arrangement,you'd rather change the caps instead of resistors,just like on guitars.Doesn't seems very difficult.I'm gonna try to locate them:NO schematic available yet for this F...... amp!(must check things on the tranny too) stay tuned!... Link to comment Share on other sites More sharing options...
Members crsnot Posted February 6, 2015 Members Share Posted February 6, 2015 Hiey Yan, check my very first post , I uploaded the schematic. I have a higher resolution one also but it's too big to upload Link to comment Share on other sites More sharing options...
Members Yan M Posted February 6, 2015 Members Share Posted February 6, 2015 Unfortunately this is the original "vintage pre-war" version(seven tubes! single PT with valve rectifier),not the reissue;but it could help...I will have a closer look.Thanks Link to comment Share on other sites More sharing options...
Members crsnot Posted February 7, 2015 Members Share Posted February 7, 2015 Ah.I didn't realize you had the original model as well as the reissue. I looked at buying a 1947 electar century but found there were several different versions.... Some had 3 inputs ,some had one. Also power ratings went from 6w to 9w to 12w as the years progressed. The one I looked at was a century case but the circuit was basically a zephyr model. I found a couple of schematics for them and also a site where the serial numbers were recorded and this helped date it however you could see from that site how many different designs were done in similar years...... Almost like they changed design around what components they could get at the time. When the original design components came available they would revert to the original design again Link to comment Share on other sites More sharing options...
Members crsnot Posted February 7, 2015 Members Share Posted February 7, 2015 Well I redid the heater wires. Since the hum didn't increase with volume I just tidied up the 6V6 wiring and only replaced the wiring from the 6v6 to the V2 and V1 12AX7's. See attached pictures. The hum is 90% gone so I guess its a success. There is still a sssshhh /Hiss (still greater than my VHT special 6 which is very quiet) but it's much better. I will try your 100R trick next. I did some research on this and some people put a 100R on each of the ends of the 2 Heater wires....you only recommend doing the + one? Scotty Link to comment Share on other sites More sharing options...
Members Yan M Posted February 8, 2015 Members Share Posted February 8, 2015 Hello:good news! mine is on the bench too(rewiring) in fact the 100R trick is for "balancing" the circuit(either one side or the other)it's more easy to "fine tune"the R setting with a pot so....The second advantage is that you can change it should you swap your tubes with new .It's up to you anyway:trial & error provided you respect basic precautions.As for schematic I just own the reissue,I was just talking about the circuit:the original(s) circuit(s) is/are more complicated than the new one:two different tubes for Mic&instrument inputs in order to provide both different gains & "colors",A layout perhaps more in keeping with your needs? anyway one can get rather close a result with just changing the caps.Good job Man!I let you know my own results Link to comment Share on other sites More sharing options...
Members Yan M Posted February 8, 2015 Members Share Posted February 8, 2015 PS:the 100R trick (whether pot or rresistor(s) is for creating a "virtual Center Tap" ,but sometimes one side is enough.A small "hiss" is quite normal and acceptable on such amps:"old days" charm! Link to comment Share on other sites More sharing options...
Members crsnot Posted February 8, 2015 Members Share Posted February 8, 2015 Good luck with the wiring it's very tight in there. I used long thin needle nose pliers like a surgeon to do the rewire around the 6v6's. They used very small gauge wire at the factory and my heavier wire was hard to fit neatly.... Well sort of neat as it was my first attempt at this sort of thing. So far on my long internet search I haven't found anyone else yet who has had a go at modifying this amp. I couldn't find the schematic anywhere either so in the end I went to the manufactures. I think the hum issue out a lot of people off. I really like the many different sounds from this amp. The combination of different inputs and then being able to vary the tone and then with or without boost switch allows huge sound variance. If it had a spring reverb.......! Plus it just looks different.The prewar century I checked out the owner said all three inputs sounded the same.... I think more for 3 simultaneous instruments rather than mic, guitar and accordian like the old Sano amps.I wonder what produces the background hiss in this amp. I read somewhere it was resistors that usually cause hiss.... Maybe resistor type? Link to comment Share on other sites More sharing options...
Members Yan M Posted February 8, 2015 Members Share Posted February 8, 2015 Overall components quality...maybe. Link to comment Share on other sites More sharing options...
Members crsnot Posted February 9, 2015 Members Share Posted February 9, 2015 Strange things occurs in designing' date='not always for the best...seen so many(good) products sunk by a 10cent forgetting.Engineers moves in mysterious ways...Fortunately,tube amps technology beneficiate from a(very!) long experience of enthousiasts: trial&error, tinkering,etc..As you said,the best option is to first rewire to best standards,then try the resistance trick.This "fixing" is harmless anyway...and costless too.As for your input arrangement,you'd rather change the caps instead of resistors,just like on guitars.Doesn't seems very difficult.I'm gonna try to locate them:NO schematic available yet for this F...... amp!(must check things on the tranny too) stay tuned!...[/quote'] Hi Yan , does the attached schematic seem similar to your prewar tube amp..its a Sano but has the 3 inputs. Also have the electar Zephyr here but not the same # of tubes...although has the three inputs.. Link to comment Share on other sites More sharing options...
Members Yan M Posted February 10, 2015 Members Share Posted February 10, 2015 Yes,thanks:looks like, althought it uses tubes more available at the time...(Zephyr:lovely name!) the SANO has an interesting onboard spring reverb circuit and seems to use the second half of a 12AX7 as a "gain oscillator" to produce tremolo.I complete the fil rewiring tomorrow(it's very late by the time i write)to be continued... Link to comment Share on other sites More sharing options...
Members Yan M Posted February 12, 2015 Members Share Posted February 12, 2015 Hello,last update:the rewiring is succesfull;no resistor needed anymore...Yet the "R" mod can be usefull for those who don't want to go so far.A tech could do the(rewiring) job within a couple of hours max ;well,extra cost & warranty lost... DIY is a much better option IMHO.thanks! Link to comment Share on other sites More sharing options...
Members crsnot Posted February 13, 2015 Members Share Posted February 13, 2015 Excellent!! The amp is still slightly noisy" but no more than a lot of amps - but it doesn't increase with volume. I am loving the tone with harmonica microphone.Such a simple fix really. So many would have been turned off the amp by the hum. Such a shame for a limited edition amp to have a basic assembly mistake. I guess we are the winners now! I got mine really cheap so even better. I hope others pick up on the fix that we have found and proven.Now all I need to do is that input impedance change ,and maybe a bit more negative feedback! and maybe darken it up a fraction more for harmonica. Link to comment Share on other sites More sharing options...
Members Yan M Posted February 13, 2015 Members Share Posted February 13, 2015 Classical "casualties" of cost cutting:cheap wiring,pots,caps...nothing structural anyway.Easy to remedy.Yet Epiphone has made big efforts to improve his quality over the last decade(s).Hope they read the posts(i'm sure they do!) and ah,let's say it:mods and tinkering are part of the pleasure on such amps,you have to "deserve" them somewhere.They're not a "plug&play" asepticized product.I got mine on sale so i think it is a (very)good value for money.As I mentionned above,I could compare with a much more expensive boutique hand wired Stimer reissue which suffered the same problem! the price of hype maybe: Stimer was Django's gear,so...In conclusion,I repeat:you can buy this amp while there are any left,and for those who did but are unhappy with,don't return them and take a few time to consider what's been said (and done!) Link to comment Share on other sites More sharing options...
Members thereminista Posted February 15, 2015 Members Share Posted February 15, 2015 Hi! I'm new to this forum. I have this issue with the epiphone amp. There is a low pitch hum when it turns on and there is a hiss higher pitched like white noise when it starts warming after about 10 seconds. If I modify the wiring as you suggest which noise will it reduce? Link to comment Share on other sites More sharing options...
Members crsnot Posted February 16, 2015 Members Share Posted February 16, 2015 Hi. Tidying up the heater wiring as posted above will remove the low pitched hum ... (Mains him). The white noise hiss is fairly typical of a lot of valve amps and will be still there. Once you start playing then is petty unnoticeable. It'd be nice to get rid of the hiss too but that may be more complex to try and fix. Link to comment Share on other sites More sharing options...
Members crsnot Posted May 5, 2015 Members Share Posted May 5, 2015 I have moved the "centre tap " wire now.....as per attached photo. This removed the last of the hum and the amp now just has a quiet hiss. Now I am having a play with the tone stack resistors to see if I can make it better suited for harmonica. Link to comment Share on other sites More sharing options...
Members mbengs1 Posted May 8, 2015 Members Share Posted May 8, 2015 i get hum only in one case. when I use a lot of distortion. Link to comment Share on other sites More sharing options...
Members Yan M Posted June 13, 2015 Members Share Posted June 13, 2015 Hello,thanks for the "center tap" update! just one thing: is it C24 or C32?(the one you show is C24) BTW I find that the amp has too much mids,sort of "honk" with P90s.Any suggestion? (tone stack caps mods etc...) Link to comment Share on other sites More sharing options...
Members Yan M Posted June 13, 2015 Members Share Posted June 13, 2015 Hello,thanks for the "center tap" update! just one thing: is it C24 or C32?(the one you show is C24) BTW I find that the amp has too much mids,sort of "honk" with P90s.Any suggestion? (tone stack caps mods etc...) Link to comment Share on other sites More sharing options...
Members crsnot Posted June 18, 2015 Members Share Posted June 18, 2015 Yes C32 definitely . I was a bit sleepy when I did the picture edit!I am trying a tone stack change to the same as my VHT special 6 is modded to take some treble off and boost base a little. I think this will reduce that mid range but not sure....I actually want the honk for harmonica use but maybe a little more bass honk! Link to comment Share on other sites More sharing options...
Members Yan M Posted June 18, 2015 Members Share Posted June 18, 2015 Ok Thanks! just what I thought...C24 is not (directly) grounded. Link to comment Share on other sites More sharing options...
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