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i'm about repair this amp , i looked over the circuit and found it run those 6L6 at a very high voltage but note sure at what current it run , so i wonder if it worth it to reduce the B+ that feed the output stage and may be best to point to point wire the circuit instead of the current PCB .
any one ever own one of these amp ?
LT
PS: any one here happen to have a complete circuit of this amp ? I only see the amp circuit but not the power supply.
Follow Ups:
Pete
I know those amps very well and they bias at .634 volts thru an 11 ohm resistor..It comes out to about 57ma per tube.The 6P3Se can take it but you can reduce the bias setting to .550 which brings it to about 50ma per tube.
There is a well guarded little secret about these amps and that is this..You can run KT88s in them without breaking a sweat.The power and output trafos are overbuilt and I run 6550s in mine and have for 6 years now..A friend of mine discovered it and we tested the filament voltage with all the 6550s installed and it read 6.45 volts which is not stressing it in the least.AAMOF,it is better to run 6550s in the amp because the filament voltage was like 6.6vac if you measure it with the 6L6gcs installed.
Now,the first thing I would do with this amp is install multi-turn bias pots. I then would change out those crappy fork pin tube sockets and put in wrap-around pin type.You then want to take out those Wimas in the outputs and put in k40y paper in oil..You need to pay close attention to the circuit board because there are lots of solder connections that should be resoldered in the power supply area..There is more stuff but that will get you going pretty well.
Honest amplification is better than excessive 2nd order distortion anytime.
Thanks Mike.
good to know the trannies can take KT88 however the load is a bit of concern here .
do you have the complete circuit of this amp ? i'm think of put the choke in the power supply ,
what do you think about point to point the circuit instead ?
Pete
You are speaking of impedance and it isn't an issue as I have done a sweep on the amp.This amp is single ended and it's even less of an issue and you can actually take out one of the output tubes,rebias and be fine.A 6L6gc biases very similar to a KT88.The plate impedance is lower but it really isn't a problem on sweep measurement and you gain an additional 4 watts per channel.
Honest amplification is better than excessive 2nd order distortion anytime.
Main issue I had was that the resistors would arc to the surface plane on the boards , right through the resistor insulation.I cured issue by heating the solder pads and pushing the resistor leads slightly up sp that there was a slight air gap to the boards.
YMMV
the one i have here is a bit more than arc . will post some photos later
Stu is correct.There are resistor issues and board warp stressing but I was going to have you do the basics first..
Honest amplification is better than excessive 2nd order distortion anytime.
Hi Mike.
look at the one in my bench now. i think the 11 ohm on one of the tube is blow and it made big mess.
Pete
I'm looking at these reworked power supplies, whatever they may be, and different/better/more expensive(?) brd caps to replace the Wima's and in every case unless it's a Sonic Craft mod w/a few Beyschlags & metal oxide resistors (SC doesn't address the bias supply regulation problem either), all the other resistors remain carbon film..!!!! CARBON FILM..!!! LOL!Doesn't this amp deserve Vishay RN65's and Dale RS series resistors (and yes the Beyschlags)?
In addition, I see the 1/2watt 10k resistors in the bias circuit increased to 2watt carbon film.. LOL! What the hell will THAT do???
FYI, besides installing 10k cermets, I changed R56 to 390 ohms and those 1/2w 10k's to 4.7k 1/2 watt metal films. (I sent this to MS in a private email).
I can regulate anything from 6-5881 to 4-KT120's (up to 60mA, but will need to do better, I just don't want to push the junk supply)..!!!
Yes, I will rework that crappy bias supply and of course the p supply as the amp still remains stock with IC electros. (uuuggghhh)...
Although the dynamics & headroom have improved somewhat, w/out having yet reworked the p supply, I'm not impressed...
Edits: 08/19/17 08/19/17 08/19/17 08/19/17
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