ashton viper 100

[geoffrod]

Hi, First time post, been a little while looking, i hope someone can give me a few pointers in the right direction.
I have a ashton viper 100 all tube amp, i know it isn't anything fancy, but it is all i can afford right now, so i am looking to change it a little, when i bought it it was fitted with 6l6's and 4 off 12ax7's,i have since changed it back to the standard el34's and at the moment i am fiddling with preamp valves to try and clean up the clean channel, being fairly new to this type of circuit i am realising that the clean and overdrive channels are using the same preamp valves even though they are on seperate channels. so how can i go about cleaning up the clean channel. will i have to change resistors and caps along the circuit around V2 and V3??????
Any suggestions would be greatly appreciated.
cheers
Geoff

[drlowlow]

Man that schematic is busy. After looking at it the values don't seem very extreme. They aren't set up for huge amounts of gain but cascaded like that might be a bit much. You could try a lower gain tube in V2 place or even V1. You could try to increase the value of R41 to lower the amount of signal into V2b triode which might be where the problem is. with this in mind you might want to check the power amp first. If the bias isn't set right it could cause distortion when the clean channel is in use.

If that doesn't work then be a bit more specific (saying that the clean isn't clean enough is a bit vague) with the problem and maybe it can be better addressed. I am not farmiliar with this amp and don't know much about it's inherent dificiencies that might cause problems. Good luck.

[geoffrod]

thanks

Thanks for a response mate,
appreciate it.
ok so i am having a little trouble with the voltages going to the power tubes, it is way, the schematic say's 444v, i have 490v yesterday, and 480v last week. the mains voltage is high where i am in oz, 252v should be 240v, the heater voltages are fine at 6.30v????
I initially thought that the voltage problems may have been coming from the fact the amp had the wrong valves in it without any changes.
i have tried to change the valve in V1 with a lower gain, but it affects the overdrive channel as well, so thought that V2 and V3 might have been a better place to do it, or like i said maybe i can increase the gain in the overdrive channel after i have changed the Valves to reduce the gain in the clean channel.
cheers
geoff

[black_labb]

in my oppinnion id probably make my own circuit or copy another amp that you like that has the same no of tubes, and use the trannies and chassis ect. i think you could end up with something thats a bit better, as these amps that try to do everything often dont sound great.

[geoffrod]

hi black labb,
thanks for your oppinion, i appreciate you taking the time.
i am not exactely sure what i would make, i bought this amp for budget purposes, with the thought that it was 100watts so surely i could get a decent volume out of the clean channel, and with the gain it has plenty of surely i could get a sound or 2 i liked out of that too.
cheers
geoff

[drlowlow]

Those voltages are well within the operating tolerance of EL34s. It might effect the bias so this is something you might want to adjust often. There are ways to make sure the heaters get the right voltages and you can look for a regulated DC heater voltage mod that will work for all kinds of amps. If not than you could use a Variac to keep the voltage at the standard 240V. Some people will be against that because it is easy to set the variac at an inappropriate voltage but it can be used.

black labb makes an interesting argument. I agree that some amps that attempt to do too much end up failing to sound good at some or most settings. Simplicity is a common method for great sounding guitar amps and this amp doesn't meet that criteria. I imagine that this amplifier uses PCBs which aren't the easiest platform to mod on. I still haven't seen a concise explanation of the problem in the clean channel. If it just is just not clean enough, I would look for the voltage divider networks that are being used in the clean channel and adjust them to not overdrive the next stage next as much as it is. another option that might be considered if that doesn't do it would be to skip one of the preamp triodes for the clean channel that is currently shared.

You might want to consider however that doing mods will reduce the value of the amplifier and if you decide it just wont work for you it might be more economical to sell and replace with something more suitible for you. Alot of people that mod and build amplifiers on this forum do so because they enjoy the journey and aren't so concerned with the economics. There are people on this forum that would pay 50% more for a 5% increase in tone quality. Before you do any substancial mods consider where the bottom line is for you.

[geoffrod]

Ok so the voltages are still ok for the el34's but aren't close to the voltages on the schematic.
when it had the 6l6's in it i couldn't adjust the bias low enough but with the el34's i can so i will just keep an eye on them.
As for a more detailed explanation for the clean channel, it isn't clean enough, it breaks up to much for me, i would like to get something like a fenderish clean tone from it, now i realise you can't make a silk purse out of a sows ear, but clean and bright fenderish style would be good.
as for skipping a preamp i had a little advice from someone about this and they suggested doing it at pin 1 on V2 and pin 7 of V3????? any comment on that.
i will continue my research as to how to adjust the circuit and where might be the best place to do so.
cheers
geoff

[John G]

Hi,
This appears to be a copy of a Marshall DSL.......with some component and tube differences in the pre amp that I believe are detrimental to the head room on the clean channel. The bias was also set incorrect from the factory.
Cheers,
John G

[geoffrod]

?????

Hi John,
could you elaborate a bit more for me on which marshall , i am not so familiar with them, which components you believe to be detrimental to the headroom, and what you actually mean by the bias is set incorrectly from the factory, are you refering to the schematic??? and the voltages on it???
look forward to your answer
thanks again for you input.
cheers
geoff

[John G]

Viper

Geoff,
I should of said that the Viper schem has more than a fleeting resemblence of the Marshall JCM 2000 series amps in particular the TSL/DSL 100 units.
There are numerous differences, the most obvious being the value of R17 on the Viper (47k) and is 10k on the Marshalls, this means that there is a much greater signal level so a 10k would be a good place to start.
You could then maybe replace V3 tube with a 12AX7 type as per Marshall.
Want more bottom end then up C6 from 4n7 to 22n etc.
I suggest you study the schmatics and note the differences, including voltages.
As to my coment on the bias voltages, I believe some run the o/p tubes too hot and the value of R147 has been lowered or my preference is to increase the value of R115.
The Marshall schems can be found at the DR TUBE site, Marshall schems, and is listed under JCM 2000.(as in year 2000)
cheers,
John G

[geoffrod]

Hi JohnG,
Thanks again for your response, i appreciate it.
Thanks for elaborating on your previous answer.
So by using a smaller resistor in R17 it isn't letting as much signal go to ground???? wont that increase gain????
and by adding another 12ax7 wont that increase the gain in the preamp as well????
i am pretty green with all of this so please bare with me.

i have downloaded the schematics you spoke about now just have to try to work them out.

cheers
geoff

[John G]

Geoff,
I bet you were a little shocked by the Marshall schems and that the circuit travels over several pages, can be quite difficult to understand. If can master these and Vox schems all others schems will pale in comparison.
I suggest you draw the TSL/DSL schems out useing the circuit flow of the Viper.
R17 is at the end of a frequency shaping network so is in shunt hence there will be a reduction of the signal at this point if R17 is reduced to 10k.
I mentioned V3 only because you may want to make up this lost level (R17=10k) by using a 12AX7 as Marshall has, then again you may have still enough level with V3 as a 12AT7.
Let the ears guide you.
Cheers,
John G

[geoffrod]

Hi John,
yes slightly overwhelming the amopunt of information on those circuits,
ok i will try what you say
i also understand a wee bit better now whay you said the 12ax7.
thankyou very much for your time

cheers
geoff

[geoffrod]

Hi JohnG,
i was removing the board out of my amp tonight ready to do a few mods, and upon finding R17 i see a wire jumped over it, what effect will this have ????
am also considering jumping a gain stage(V2B) using a dpdt switch at C31 to C32, any comments as to whether this is viable????

cheers
geoff

Geoff,
I bet you were a little shocked by the Marshall schems and that the circuit travels over several pages, can be quite difficult to understand. If can master these and Vox schems all others schems will pale in comparison.
I suggest you draw the TSL/DSL schems out useing the circuit flow of the Viper.
R17 is at the end of a frequency shaping network so is in shunt hence there will be a reduction of the signal at this point if R17 is reduced to 10k.
I mentioned V3 only because you may want to make up this lost level (R17=10k) by using a 12AX7 as Marshall has, then again you may have still enough level with V3 as a 12AT7.
Let the ears guide you.
Cheers,
John G

[John G]

Geoff,
Looks like someone had the same idea, is the bridged resistor a 47k ?, and does it look like a factory mod or after sale one ?
As other posters have already suggested make sure all the voltages around the pre amp tubes are correct......and that the right tubes are fitted. It is very difficult to advise you as to where to from here without having a unit in frontof me. My only other thougt is that the boost 'FET' device under R17 is not switching and is in boost mode all the time.
Maybe you need to take it to a service tech who has all the tools etc and get the headroom checked with test signals and a scope.
Bypassing a tube stage is an option, but it sounds a bit drastic at this stage.
Sorry for the lack of help.
Cheers,
John G