Sunn 190L head mods - info needed

[tjm]

i've got a 190L head that I'm having some work done to and I need some info:

does anyone have a schematic for these?

also, can anyone offer any info about the following mods?

-conversion from 6550 to EL-34
- master volume  mod that is transparent when cranked
-bypass switch for reverb and vibrato
-revoicing the EQ section
-changing mid-boost switch to bass boost
-replacing worn/out of spec caps/resistors, etc.

if anyone knows of any others i should consider or that they have experienced please let me know...I'm just trying to research these potential mods or any others that might exist. i played an el-34 sunn guitar head and preferred it to the 6550's for the kind of stuff i play.

thanks!

[tjm]

can anybody help with this???

-thanks

[Fred Cook]

You preferred an EL-34 amp to a 6550. So do most people - one reason that Sunn amps were never that popular with guitarists.

Converting a 6550 Sunn to run '34s is possible, but a lot of work and a bad idea. No matter what tubes you run, a Sunn is still a clean amp. I had a Solarus which used '34s. The fact is that the Sunn is an outgrowth of a super clean dynaco hi-fi amp.

Were it me (and it was) I would run the beast on KT-88s - most people claim to hear a difference - and get the overdrive pedal of your choice. I use a RT-66 and a TS-9.

Failing that, sell the beast and get a modern, low watt, higher distortion amp.

DiploStrat

[tjm]

thanks for the info fred,

actually i already have a KT powered sunn, it's cool.

i played a friends 60 watt Sunn head that was converted to el-34's and liked it....so I'm gonna give it a go.

before i dive in i'd like to at least have a schematic, which is what this post is really about...that and maybe any mod ideas floating around....

[Anonymous]

An EL34 mod shouldn't be too difficult.  The EL34 has (I believe it is...) the supressor grid on pin 1 or 8 and the cathode on the other.  The 6550 has these two elements tied together internally.  Hopefully neither of these pins will be used to hold "other" circuit components, and if that is true for your amp, simply solder a jumper between these pins for each output tube.  If you fail to do this, you won't get much output from the EL34's

You will have to rebias the amp.  Hopefully the stock bias adjustment has sufficient range.  If not, it may have to be modified by changing a resistor in the network.

After that... Rock On!!

As for a schematic, I have never seen one... but it should be close to something like the 100S with reverb and tremolo.

[tjm]

thanks for the info guest!