VASE HYBRID 100

[TIMBO]

Hi guys, I finally score a local icon that is made in my home town of Brisbane.
Here is a bit of info.
http://www.vase.com.au/about.php
This one has jumped ahead in the restore queue, as I an eager to give it a blast.
It's fairly stock with a new IEC plug and a couple of minor mods.
I have not turned it on as there is a couple of resistors that are showing some signs of overheating.
One is across the mains switch (1k)
The 220r paralleled with a 10k for the bias supply.
Bleed resistor changed from 120k to 150k and evidence of some scorching around this area.

The earth connection from the IEC NOT bolted to the chassis.
I'm hoping some new Ecaps will do the job.

[TIMBO]

Couple more...........
http://www.ozvalveamps.org/vase.htm

[tubenit]

THANKS for sharing about this amp!  Very cool bit of history with it.  I enjoyed reading about it. 

Hope you get it back working to all it's glory.   

Sort of reminds me of the MusicMan amps (I owned a RD50 112 hybrid which had very nice clean tone)

With respect, Tubenit

[TIMBO]

Thanks T.
I have a few of these 100 watters (KT88/6550)and they all are pushing the output tubes to the max to get the claimed 100w.
It seems that 100w is not really needed and to trim the output back to a more useable 50-75w would be great and hopefully save the old tubes.
All have fixed bias and I know that I could just bias them cold and leave it at that, is going to a cathode bias going to give me a more useable output???

As expected it has the old type rectifier diodes, do these need changing.Thanks

[sluckey]

Lowering the screen supply voltage is an easy way to lower power, at least on paper or keyboard. Actually doing so may be a bit more involved, depending on the power supply. Using a simple VVR type circuit to reduce only the screens is one option. This is what I'd try if the power supply is not set up to easily drop screen voltage. Or, you could use a couple power resistors and a filter cap to make a voltage divider for the screen supply node.

Connecting the screens to the plates to run as a triode is another way to reduce power, but you may not like triode mode.

Converting to cathode bias and using a large cathode resistor to bias cold may get the power down enough for you.

[TIMBO]

Thanks Sluckey,Having a choke of approx. 450ohms means that the screens are close to the plate voltage, I have not juiced her up yet to take voltage readings to see how close they are.
Your suggestions noted and i'll get it up and running and try them. thanks

[trobbins]

You could consider taking the screen choke to the doubler mid-point.  I have over 500V on that doubler in my PA100.  That is with the 250VAC mains tap, but as the heaters are 6.6V, then the 240VAC tap wouldn't be good.  The choke will minimise the sagging, so screen voltage shouldn't fall too much more than about 260-270V, which is pretty text-book for a KT88. 


Don't forget to take care with the 'high side' doubler cap.  I have lots of 470uF 450V, so that meant the main filtering caps doubled in size.  Definitely fuse the secondary winding.  The old diodes are circa 1970 so should be still ok, but I'd recommend using 2x UF4007 in parallel as a replacement for each - the doubler, along with larger capacitance, is quite stressful.


I installed a little fan behind the OT - out of sight, and low flow, but enough to lower the oven temp.

[TIMBO]

Thanks Tim.
I did a few mods just to bring it up to scratch on the safety bit.
This one fired up well with an alarming 575v on the plates/screens.
With this voltage I was unable to adjust the bias to give a comfortable 70% bias, it was up around the 95% mark.
With the PT spec sheet there is three secondary taps that measured about 10v above the spec and I was able to use these taps to reduce the B+.
For the moment I settled on the lowest tap, then I was able to adjust the bias to 70%.
I am able to rewire the screens to the mid point of the doubler, hopefully this will give the valves some relief and also reduce the power output, or I will add a 1k resistor to the screens.

[TIMBO]

Hi guys, I tried connecting the choke to the mid point of the doubler and it was not very successful,just made a distorted blatty sound 
Anyway, reconnected choke to top of doubler and added a fuse between the rectifier and the main caps.
Changed the screen resistors from 220r to 1k/5w.
Changed the 1k across the standby sw. to 180k.
Added two more speaker jacks and labelled them so that the 8ohm is 16, 4 is 8 and 2 is 4.
Some time in the future i'll get a good matched pair of KT88's as these are showing the cathode readings are a bit off. 

[trobbins]

Not the best gnd point for the output tubes Tim

[TIMBO]

The grounding for those tubes are connected to the wire that was originally connected to them and not just relying on the bolt holding the tag strip.

[trobbins]

If possible, it is good to aim for no ground loops.

[TIMBO]

Hi guys, This one is completed but may have some issues.
Gave it a good working for about an hour and what a narly amp.
It's got a very vox bite clean and loud with very little hum and fizz, dead silent at idle.
We used a firebird copy with hot humbuckers and got a very loud clean chime when finger/pick picking, but dig in with the pick (no control adjustment) this thing just kicks ASSS.
It was unbelievable the change, power chords were thick and strong with no mush.
A strat was used but not very convincing.
LP with p90s was good but not as good as the buckers.
Overall very happy.
The issues, brought it home to do a final clean and touchup, with only one small job to do and that was to change the speaker jacks, simple.
Testing the final job and all I get is a low volume distorted sound.
Checked all voltages and are good.
Tapped around to find any loose joints,good.
It may be something to do with the power tubes being un matched. 
OR even some of the components at their end.
I checked the speaker jack and all seem good.
Anyway hopefully I will get some new KT88s soon and eliminate that as the problem. Thanks

[TIMBO]

Hi guys, New tubes arrived and where sounding good.
Just a couple of things...........
Changing to cathode bias and the output I could expect
The amp has a good range of tone but there is an excess of base that gets really ugly and flabby. The two inputs are quite different with the 1k it is some what distorted and does put a bit of hair on it but really delivers way too much bass.
The other input is much cleaner and I am able to turn up the volume with out too much distortion.
I feel that at the higher volume it wants to feedback.
I like the 12AX7 in the PI as it does add some nice hair whereas the AT7 tends to get a bit too fuzzy.
I changed the speaker output so that an 8ohm load is in the 4ohm tap.
I'm using a guitar with humbuckers so maybe that is not helping. Thanks

[trobbins]

Perhaps lower the 0.1uF coupling caps from PI to output stage.

[shooter]

with the 1k it is some what distorted

Kinda *arm-chairing* it here, it looks to me like the 1K input would be hotter, does that CH *clean up* if you roll back on the guitar?   Do the tone controls work well?, seems like the bass pot might need to be bigger?
Might try changing the coupling cap from the last transistor into the PI from .01 to .0047 as an experiment.

[TIMBO]

Thanks guys, i'll give those ideas a try.
As a side note I picked up this SS amp that have been built by the same maker and tracing out the preamp circuit is pretty much the same but has 120k on the inputs, so I may try that as well.