Just got my X101B back...

Spent a couple hours last night, got the PT and cans installed. This morning I tried to fire it up. Brought up the power slowly, and no drama, but it's not working. V1, V6, V2 & V7 aren't lighting up. I checked all four tubes had good filaments, and spot checked a few things, nothing obvious stood out. SAMS schematic shows 45v at pin 5 of V1, I have about 6v, which makes sense since V1's pin 5 goes back to the junction of R99 & R100, which is basically the brown/white 6v winding? The first thing across the 6v winding is the pilot light, which is working, and the filaments of the output tubes and V3 & V8 are lit as well.

V1,6,2&7 are in series, but I don't quite see where their voltage is supplied from.

I'll dig into it more later.
 
V1, 2, 6, 7 form the cathode resistor for the output tubes. If any one of those tubes is open, it will not work, if the output tubes aren't conducting any current it won't work either.

If you've got no voltage at pin 5 of the output tubes, that sounds like you've got no significant B+ to the output tubes, and/or no screen voltage. Check pin 3 and 4 on the output tubes and verify you get about 425 on pin 3 and 380 on pin 4.

If no joy there, revisit the power supply and check for appropriate voltages at the cans.

http://akdatabase.org/AKview/albums...01-B Service Manual Ser No_ 70001 - 79999.pdf
 
Well, turned out to be an especially cruddy tube socket. Amp is currently jamming out some tunes on the workbench after about a 35 year hiatus! Something still not 100%, doesn't have much volume, voltages are kind of low. Only seeing ~ 700v off the red winding. The schematic shows 790v. PT is currently around 100 degrees F. I remember it used to get warm, but don't know how warm is normal. Due to low voltage, maxing out the bias control only gets 32v of bias. What's there sounds pretty solid though, not distorted.
 
Whats the heater voltage?

Is the B+ winding the same on each side, meaning if you use the chassis as ground, are you getting about 350v on each leg or is one leg considerably higher?
 
B+ center tap is grounded to chassis, and between either side of the winding to ground is 350v. Heater voltage is low @ 4.9v. I disconnected one side of the winding to see what the no load voltage is, only 5.36v.
 
Check the other heater winding unloaded. I'm thinking you've got the two reversed.
It's totally possible they got the 5.0 and 6.3 winding color's backwards.
ScreenHunter_82 Jul. 04 21.10.jpg
 
Check the other heater winding unloaded. I'm thinking you've got the two reversed.
It's totally possible they got the 5.0 and 6.3 winding color's backwards.

Good Call Larry - 7.02V. Was easy enough to check that one, just pull the rectifier tube. I'm going to be glad I routed the xformer wires in such a way as to leave enough wire to work with.... Guess I'll be swapping them...
 
BTW, the official Fisher schematic is much more gooder then the SAM's. Much better layout. I've noticed that over the years with SAM's, guess they had to make sure it didn't look like plagiarism ...
 
Swapped the windings - That totally made the difference. Plenty of volume, filament voltages are where they should be, and plenty of bias voltage. B+ steady at 715 volts. What's a normal range of operating temperatures for the power transformer in these beasts?
 
The other big fear with swapping the leads is the 6.3v winding is usually not insualated for as much voltage as the 5v winding is. The 5.v rectifier winding has to carry full B+, so ~400vdc. The other one is usually pretty near to ground potential. Also to guess at it, the 6.3v winding probably has more current capacity since its running more than one tube with a 2 amp heater. That will make a fair bit of heat in the transformer.

Under about 150F is considered OK. The cooler the better of course.
 
I talked to Heyboer this morning, their specs were derived from info somebody gave them at some point over the years. He corrected it based on our conversation. As to dielectric strength of the insulation for the 5v vs 6.3v windings, both wires have the same 600 volt rating. I'm not certain that it's worth removing the transformer and sending it back.

Has anyone incorporated a silent muffin fan to cool the gear?
 
if they're both properly insulated, no worries. It wasn't always the case in the olden days. Just make a note on your schematic about the wire colors being reversed or whatever the case is.
 
My 101-B P.T. tends to run about 130*F after warming up to that after an hour or so. The outputs about 125F. Dave has noted in previous posts that 190*F would be absolute max temp with gross failures shortly thereafter. But I would think anything under 160*F would be ok. Remember hot water straight from the sink can run anywhere from 120*F to 160*F depending on thermostat setting. Most water heaters are set for 120*F for at least 10 years now from the factory which can cause 1st degree burns and or slightly into the 2nd degree category(blistering) if set to HOT ONLY. So the hand is a very poor gross indicator of temps. Hot water used by Physical Therapists is no hotter than 105*F which can get initially a little uncomfortable if you are in a full body tub for P.T. A 5 to 10 count of your palm on the top of the transformer would indicate usually from 120-125* unless you've got really thick palms and or are used to it.
 
I use either infrared thermometer or the type K thermocouple and my fluke dmm. It was up to about 105F last night. Setting a muffin fan next to the chassis knocked it down by 18 degrees.
 
105*F isn't gonna hurt anything. Leave the fan off and run it for 3-4 hours at a volume of about 10:00. Check it every 1/2 hour for temp stability. If it doesn't go much higher and stabilizes after 2 hours or so, don't worry about it. It's probably NOT going to get hotter than that. But if you worry about it in the back of your mind put the fan on from the side next to the PWR X-frmr and have it blow across the unit.

This is an extreme example but shows what can be done with a "HOT RUNNING" 7591 receiver/amp.

Everyone on the Sansui Forum crams the "if you have the cover on you MUST use a fan for the 1000A", down everyone's throat! I found that the problem is not the transformers or the Output Tubes so much as it's the heat given off by the 300v drop that the large 30A resistors have to handle constantly and their location. (See illustration below). Plus anytime EH7591's are used airflow is actually restricted by the tube envelopes. As these were the only NEW plug & play 7591 replacements at the time 10 years ago it makes sense, but with the Tung-Sol's or Old Stock Westinghouse, or other brands airflow is normalized but also still somewhat restricted between the tubes and all X-frmrs but more so on the side at the pwr x-frmr. There are minimal air holes in the chassis, and the bottom has slots 1/2 way across. Old Resistors shown in Turquoise, NEW Replacement resistors in ORANGE on illustration.

I took some Solid Aluminum Hi-Wattage (50W) 12Kohm (x4) and a 600ohm 50w Dale resistors, rewired so they were spread out on the chassis, away from the transformers and output tubes. One pair was placed on the separator plate behind the P.T., but the rest (3 Total) were placed on the front cover behind the tuning string. The temps were now spread out all over the unit vs. all the heat in the back between the transformers. Temps on the PT dropped 20degF to 130*F and the output in the center dropped about 5deg DegF..

Then I installed Tung-Sol 7591 Re-Issues (Original size bottle) against the Large bottle EH's. Temps across all transformers dropped another 10-15DegF. So now with the Tung-Sol's the P.T. is running about 120-125*F and the output's are a relatively cool 105*F. There is plenty of room between the tubes, and transformers to facilitate airflow. One last thing I did was to get a roll of 3" Aluminium HVAC Seal tape (Duct Tape). This is placed on the end-bell's or winding sides directly facing the tubes. Some of the Radiant heat from the tubes is reflected back to the tubes or the air space btwn the tubes, and the transformers. Now instead of less than 1/2" of space btwn the tubes and Xfrmr's, it's over 1/2" and airflow is actually able to go thru the unit rather than being restricted some by the EH7591a tubes.

sansui 1000a tube layout.jpg


BEFORE Note how close resistors are to tubes and X-frmr Tubes are my EICO Test mules.
100_1149.jpg


AFTER Note the increased room btwn the tubes and X-frmr
100_4262.jpg

With Tung-Sol 7591A Re-Issues, this 1000A is now cooler than my 800c's and my 400's. NO FAN's, even with cover on top. Heat output overall is now the approx the same, but it's not concentrated at the back of the unit. Overall the cover is very warm, but it's actually cooler due to spread out sources and physical heat-sinking of the resistors where as before they depended on airflow. I normally run it naked, but when the grandkids come over, it gets the cover put on. But there is no need for a fan now.

With the 101-B, If you do add a fan, place it on the power x-frmr side and have it blow across the unit from the side, the air blowing btwn the shield and the x-frmrs. Clean up and polish the shield btwn the output tubes and X-frmrs. I don't see a need for the HVAC tape at this time. As cool as mine runs with Wall voltage to as high as 124V I don't anticipate that your's will run much different with a new transformer.
 
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Nice thermal management Larry! I remember this 101-B heating up my bedroom back in the day... I'm probably not going to worry about it. I just need to find a case for it now, or have one built... Also time to start hunting for a decent set of vintage speakers.
 
Excellent! Congrats.
I am looking at a 101 - ST version that is apparently in original working condition. Already have a TA600 receiver so not sure I will act on it.
7chord, you should become a paying subscriber so you can post a WTB in Barter Town for speakers. Depending where you are located you could get some great options.
 
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