Do as I say, Not as I do!
My only child is 31 and 2800 miles away.....the grandkids live with her, safely out of the way. The last cat died of old age about 20 years ago.....And my fingers are on the KILL button!
JUst came in to watch the end of the football game.....The Dolphins (local team) just beat the Seattle Seahawks (my daughter and her husbands home team)....the text message trash talk has already stsrted!
Been sorting tubes all day. I did find even more 813's although some have paint on them. Got a zillion 6L6 types, maybe it's time to melt some metal ones, haven't done that since high school. I also have more 6146's than I thought, maybe 10, so they need testing. Found a bunch of 8068's rare and expensive tube, can't melt those.
Todays tube sorting adventure yielded several interesting specimens to play with. Did I hook up some of the 6V6's.....OK, 6L6's...no??? OK, how about the biggest tubes in the box....YEAH, thats the ticket. Actually I just hooked them up to a power supply to see if they were any good. Well, I have good news, and bad news. The good news, one tube biases up properly, and the grid does actaully control the plate current. The bad news, the other tube is gassy and will draw current even with a cold filament.
Can you tell which is which?
Can you tell which is which?
Attachments
I too, couldn't decide what to wire up next. When I got home from work tonight, it became a bit clearer. There were two boxes at my front door. One box contained one of the toroidal power transformers shown in post #109. It looks a lot BIGGER in real life. It should have no problem melting a bunch of sweep tubes....all at the same time.....which brings me to the second box. It contained 150 13GB5's, 50 sockets, and 50 plate caps. Now the only question is how many of these guys do I connect together!
There are several flavors of 13GB5's / XL500's. Most seem to be the usual Mullard design made in Holland, and the UK. There are 18 that look Japanese, but are labled "made in Korea." They are smaller and look easy to MELT.
George, I see the 13GB5's on sale at both Rogalski's and ESRC. Where did you get yours and it sounds like a mix of manufacturers from one place, correct?
PS, the transformer guy has two listed for $90 with free shipping now. I just pulled the trigger...I guess I need to go look into power factor correction for the house.
PS, the transformer guy has two listed for $90 with free shipping now. I just pulled the trigger...I guess I need to go look into power factor correction for the house.
George, I see the 13GB5's on sale at both Rogalski's and ESRC.
Mine all came from ESRC. I had over $300 credit with Stan that I needed to use by the end of the year. I had walked into his shop back in March or so handed him a $10 bill and asked for 10 13GB5's. They were all Sylvania's in good looking yellow boxes.
This time I called in my order and had them shipped. I received a random mix of assorted brands. Some were in less than great condition boxes. Some were falling apart. All the tubes look new and all except for the Korean tubes are actually Mullard, built in Holland or UK regardless of the brand screened on the glass. There were a few Mullard/IEC branded tubes too.
I ordered 1000 tubes from Rogalski's earlier in the year and received a similar mix of random brands in old boxes.
Rogalski was the originator of the $1 sale, and ESRC just matched it. Both had the same list about 5 years ago, but the lists diverged as inventories dwindled and type numbers were removed. The intention was to clear out the warehouses of tubes that never sold well.
A few people here at diyAudio figured out how to make cool stuff with some TV tubes in ugly old boxes. The 13GB5 may be the last tube on the list capable of cranking out some respectable audio power. There used to be several.
Mine all came from ESRC. I had over $300 credit with Stan that I needed to use by the end of the year. I had walked into his shop back in March or so handed him a $10 bill and asked for 10 13GB5's. They were all Sylvania's in good looking yellow boxes.
This time I called in my order and had them shipped. I received a random mix of assorted brands. Some were in less than great condition boxes. Some were falling apart. All the tubes look new and all except for the Korean tubes are actually Mullard, built in Holland or UK regardless of the brand screened on the glass. There were a few Mullard/IEC branded tubes too.
I ordered 1000 tubes from Rogalski's earlier in the year and received a similar mix of random brands in old boxes.
Rogalski was the originator of the $1 sale, and ESRC just matched it. Both had the same list about 5 years ago, but the lists diverged as inventories dwindled and type numbers were removed. The intention was to clear out the warehouses of tubes that never sold well.
A few people here at diyAudio figured out how to make cool stuff with some TV tubes in ugly old boxes. The 13GB5 may be the last tube on the list capable of cranking out some respectable audio power. There used to be several.
I received two of the power toroid transformers I mentioned in post #109 of this thread. Attached is a pic of the actual measured no load voltages as well as the resistance of the windings for those that wish to model power supplies.
This thing runs on the high side, but it was rated for 115 volt input and I measured at 120 volt input with paralleled primaries.
I also put a 3.2 amp resistive load on the 16.6 volt winding. Even though it is only rated for 2 amp, it only dropped to 16 volts under this load. Four parallel 13GB5's will need a series dropping resistor.
Finally, it is potted in the middle but I wish it wasn't so windings could be added or removed; however, it looks like removal of this potting may not be too difficult.
This thing runs on the high side, but it was rated for 115 volt input and I measured at 120 volt input with paralleled primaries.
I also put a 3.2 amp resistive load on the 16.6 volt winding. Even though it is only rated for 2 amp, it only dropped to 16 volts under this load. Four parallel 13GB5's will need a series dropping resistor.
Finally, it is potted in the middle but I wish it wasn't so windings could be added or removed; however, it looks like removal of this potting may not be too difficult.
Attachments
I have one of them but I haven't measured it yet. Did you find any extra "goodies" in the box with the transformers?
I am thinking it will be easier just to add an extra transformer for heater power.
I have reconnected the 13GB5's to the driver board for a few more measurements. If things work out, I may venture far outside the norm, maybe to the edge of insanity, for the next experiment......
The weather is nice, so I need to drag the drill press outside and make some holes........
I am thinking it will be easier just to add an extra transformer for heater power.
I have reconnected the 13GB5's to the driver board for a few more measurements. If things work out, I may venture far outside the norm, maybe to the edge of insanity, for the next experiment......
The weather is nice, so I need to drag the drill press outside and make some holes........
P.S. If anyone wants a few 6FW5s for this project let me know. I bought a big stash of 38 of them for $4/ea. I shouldn't have bought them all (didn't mean to hoard) but a moment of euphoria came over me. I'll sell them for what I paid. I am in Toronto, so shipping might bite a little to the US.
They seem like they'd be nice tubes for this and I'd like to try myself.
They seem like they'd be nice tubes for this and I'd like to try myself.
That didn't turn out like I intended......The weather in south Florida can flip in an instant......and it just did. I was outside drilling holes when I heard the phone ring. I had been inside about 5 minutes when I looked outside to see it raining...hard. So now one of Pete's driver boards is drying in the oven and my drill press is drenched in WD40. *&^%#(#!!!!
For those who don't know, the 6FW5 is an uprated 6AV5 and should work well here. The original 6AV5 started out with a 12 watt plate inside. As TV's got bigger, manufacturers pushed the tubes harder and harder. The tube manufacturers responded with bigger plates inside some tubes. The 6AV5 could be found with 12, 15 and 17 watt plates inside. A consumer could stick a 12 watt 6AV5 into a Tv that really needed a 17 watt tube, so GE gave their 17 watt 6AV5 a new number, the 6FW5.
I got 10 of these from the same place Josh got his tubes. I have seen them make 100 watts per pair in a slightly different circuit with a 3300 ohm load and 550 volts of B+. They are octal tubes with no plate cap, but a unique pinout. I have not tried them, or any octal tubes with this driver board yet.
An update from my side:
I am progressing with a monoblock design using this board and 12HL7 pentodes that should work for both triode connected KT88 or pentode connected single or parallel 807s.
I am planning on using an off-the-shelf replacement guitar amp power transformer:
Marshall 100W Plexi Laydown Style 100W Power Transformer ClassicTone 40-18046
Datasheet: http://www.classictone.net/40-18046.pdf
This transformer is perfect to generate 250V (for the driver stage and also screen grids of 807s) and 500V (for the plates) using a full-wave bridge plus centertap solid-state rectifier. It also has a floating bias winding which is ideal for this PCB to generate the negative voltages. And enough filament current to light up a pair of KT88's or 4x 807s plus the driver tubes.
I've designed a power supply PCB to hold the rectifiers and capacitors. I'll post some more info on that when I get it built in a few days.
As for the OPT, I thought I'd try reproduction Dynaco A-431S, which is 4300 ohms and good for 60W @ 20Hz, or 120W @ 30Hz. It's a beefy chunk o' iron:
A431S Triode USA Output Transformer for Dynaco 4300 Ohm 60W/120W for Dynaco MADE IN USA
Will post more as I get it on the bench...
Pete
I am progressing with a monoblock design using this board and 12HL7 pentodes that should work for both triode connected KT88 or pentode connected single or parallel 807s.
I am planning on using an off-the-shelf replacement guitar amp power transformer:
Marshall 100W Plexi Laydown Style 100W Power Transformer ClassicTone 40-18046
Datasheet: http://www.classictone.net/40-18046.pdf
This transformer is perfect to generate 250V (for the driver stage and also screen grids of 807s) and 500V (for the plates) using a full-wave bridge plus centertap solid-state rectifier. It also has a floating bias winding which is ideal for this PCB to generate the negative voltages. And enough filament current to light up a pair of KT88's or 4x 807s plus the driver tubes.
I've designed a power supply PCB to hold the rectifiers and capacitors. I'll post some more info on that when I get it built in a few days.
As for the OPT, I thought I'd try reproduction Dynaco A-431S, which is 4300 ohms and good for 60W @ 20Hz, or 120W @ 30Hz. It's a beefy chunk o' iron:
A431S Triode USA Output Transformer for Dynaco 4300 Ohm 60W/120W for Dynaco MADE IN USA
Will post more as I get it on the bench...
Pete
This is very interesting ...
12HL7 is the driver that I have, and a PCB for the power supply is very comfortable and tidy.
For the iron I'll go with EDCOR, for the OPT will be the CXPP-MS-6.6K (I have them at home) and for the power XPWR002-240, would it work? if not so, what would be the appropriate specifications?.
I prefer to order a custom transformer and coincide with the OPT, also not be more expensive than the ClassicTone.
12HL7 is the driver that I have, and a PCB for the power supply is very comfortable and tidy.
For the iron I'll go with EDCOR, for the OPT will be the CXPP-MS-6.6K (I have them at home) and for the power XPWR002-240, would it work? if not so, what would be the appropriate specifications?.
I prefer to order a custom transformer and coincide with the OPT, also not be more expensive than the ClassicTone.
That seems to be a bit of a religious issue...
I don't think it's necessary to regulate the screen voltage on power tubes. In fact I would prefer it scale with B+, so if the B+ drops so does the screen voltage.
There are cases where I've seen it desirable to intentionally make the screen voltage have poor regulation - like by using a shared series resistor. In one case I found that this decreased distortion significantly, though I never bothered to figure out why.
But I'm sure there will be disagreement
Look back two posts... the circuit I plan on using generates B+ and B+/2 using a bridge rectifier and center-tapped transformer... so in my case I'm planning on 500V and 250V.
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