Tube Amp Find

[rossm]

UL stands for ultra linear, which means there are connections to the grids (G2 mentioned above) as well as the anodes ('plates' in the US). These are pin 4 and pin 3 respectively on the KT66. Pins are numbered clockwise when viewed from below.

Great find, by the way.

Thanks for clearing that up for me.... I have always wanted to own a HiFi Tube amp... Lots to learn here...

 

[primosounds]

Good news !
It looks like the output transformer is good, Correct me if I am wrong though...
Input Side
Center Tap (Red) -> Blue/White = 118 ohms
Center Tap (Red) -> Blue = 211 ohms
Center Tap (Red) -> Brown/White 105 ohms
Center Tap (Red) -> Brown 212 ohms
Blue -> Brown 425 ohms

Anything else I should check ?
Thanks for everyone's help !!!

Alllrigghhttt!!! That looks like it should be. The OPT is by far the hardest part to find if it goes bad.

 

[knockbill]

They possibly tried 6V6s as the new PT couldn't run the 6L6s... the original OPT wouldn't be proper, as was already said, tho...

 

[Brice]

Use TungSol KT66. They run fine in this amp. They draw less heater current so it's easier on the PT.
They are in fact a 6L6GC in a big boy bottle. Look awesome.

 

[PakProtector]

The 'right' power trans is hard on things due to its excessive voltage. a solid 360-0-360 will deliver low-mid 400V of B+ and that is more than adequate.
cheers,
Douglas

 

[AdamAnt316]

The 6V6 is a vastly different tube than the 6L6. All the two sixes tell you is that the tube has a 6.3V filament, and uses six elements (filament, cathode, beam plates, two grids, and plate). The 6L6 was the first, and largest, in a series of beam-power tetrodes introduced in the early '30s. The 6V6 was smaller, as was the 6F6 (actually a power pentode), 6K6, 6Y6, and others. Also note: while the 6V6 has equivalents with different filament voltages (5V6, 12V6, etc.), the 12L6 and other xxL6 tubes are NOT at all similar to the 6L6! Well, they're still beam tetrodes, but attempting to run a 12/25/35/50L6 as you would a 6L6 would probably result in a smoldering octal base where the tube once sat..........
-Adam

 

[PakProtector]

AdamAnt, do please explain how the KT88 has a 6.3V heater... per your numbering convention...or the KT77 for that matter.
cheers,
Douglas

 

[AdamAnt316]

AdamAnt, do please explain how the KT88 has a 6.3V heater... per your numbering convention...or the KT77 for that matter.
cheers,
Douglas

KT88 is not a standard US tube designation using the RETMA numbering system. GEC/Genalex, who developed the KT66 and KT88, had their own numbering system which didn't correspond with anyone else's (for example, their version of the 12AX7 was known as the B759). The KT stands for "Kinkless Tetrode", i.e. the beam-power configuration as originally used with the KT66 (aka 6L6). The KT88 was never given a RETMA designation in the US; instead, it's generally cross-referenced to Tung-Sol's 6550 (which used the 'industrial' numbering system, for whatever reason).

Before you ask about European tubes, they had a designation system of their own, which used a different coding. In their system, the filament voltage was indicated by the first letter, with E representing 6.3V. Note that said letter does not always denote a specific voltage; rather, the higher letters actually denote the filament current, i.e. for tubes used in a series string a'la AA5 radios. The letters after the first designated the element(s) used inside the tube, with the numbers after the letters denoting the number in the series. For example, the EL34 has a 6.3V filament, contains a single power pentode section, and was designated number 34 in the series. More on these numbering systems (and others) can be found here.
-Adam

 

[GordonW]

Yep looks my transformer has the wrong voltages, HV of 375v and I need 425v.
Not sure what to do now, Anyone have a good source for an R13 or Stancor 8412 or any other transformer that would work ?
Thanks

If you want to go ahead and test/fix everything else, there is one way you can get your B+ voltages up very close to what they would be with the original power transformer.

If you sub a 5AR4 rectifier tube for the 5R4GY, it will bring the DC B+, with 375VAC on the PT, up to around 95% of what it would be with the 425v original power transformer with the 5R4GY. It'll be just a little lower voltage than stock, but within close enough to work properly.

Regards,
Gordon.

 

[GordonW]

Frist nice find ! Your provided meserments show Allan got The output tubes are not really interchangeable it will work but the 6v6 is not as a high enough power and will limit the amont
Of power output .

The 6V6 is also not made to handle the over-450v B+ voltage inside the W5. You can sometimes get by with some tubes, but some will self-destruct under that much voltage.

Yes, I know there are guitar amps with 450V using 6V6s- but they are designed with more power supply sag, less plate current, and other protections for the 6V6s, than would be found in a W5. And, even with those, you have to be very careful which 6V6s are used in them...

Regards,
Gordon.

 

[rossm]

KT88 is not a standard US tube designation using the RETMA numbering system. GEC/Genalex, who developed the KT66 and KT88, had their own numbering system which didn't correspond with anyone else's (for example, their version of the 12AX7 was known as the B759). The KT stands for "Kinkless Tetrode", i.e. the beam-power configuration as originally used with the KT66 (aka 6L6). The KT88 was never given a RETMA designation in the US; instead, it's generally cross-referenced to Tung-Sol's 6550 (which used the 'industrial' numbering system, for whatever reason).

Before you ask about European tubes, they had a designation system of their own, which used a different coding. In their system, the filament voltage was indicated by the first letter, with E representing 6.3V. Note that said letter does not always denote a specific voltage; rather, the higher letters actually denote the filament current, i.e. for tubes used in a series string a'la AA5 radios. The letters after the first designated the element(s) used inside the tube, with the numbers after the letters denoting the number in the series. For example, the EL34 has a 6.3V filament, contains a single power pentode section, and was designated number 34 in the series. More on these numbering systems (and others) can be found here.
-Adam

HI Adam,
Thanks for this info on tubes !!!!

 

[rossm]

HI all
Thanks to every one that replied, lots of good info for sure. After looking at prices on restoring this little amp I have decided to put it on the back burner. I would love to get it working but am looking at $400 to $500 in parts, plus I have several restorations currently in progress. Once time and finances allow I will be back...

 

[Dandy]

Given that the transformers are okay, why so much for parts? I'm just curious, not questioning your decision to postpone restoration.

 

[crispycircuit]

Maybe the rent's due...

 

[Dandy]

Maybe the rent's due...

Yes. I just hope the OP hasn't been put off by looking at a boutique parts pricelist. Caps of spun gold, resistors of finest ivory, etc.

 

[maxhifi]

Against all good sense, long ago I did try 6V6s in an amplifier with 450V of B+, and adjustable fixed bias. I had a whole bunch of pulls, and the amplifier was well protected.

Regular 6V6s with the smoked glass tend to arc over and self destruct, but the Sylvania 6V6GTB held up and sounded great. This was 20 years ago though when used 6V6s were super cheap, I would not try this today! This is beyond living dangerous, is likely to just ruin tubes.

 

[rossm]

Hi
Here is the list of parts I compiled for the amp, please correct me if I have gone over board for the parts.
Mouser caps and resistors $80, see attached pdf.
Antique Electronics supply for multi-can caps see below $70.97

Capacitor - CE Mfg., 525V, 20/20/20µF C-EC20X3-525 1 × $31.41 $31.41

Insulator - 4 Section, for FP Cap S-H120 1 × $1.95 $1.95

Capacitor - CE Mfg., 525V, 40/40/40uF C-EC40X3-525 1 × $33.11 $33.11


Power Transformer $100
2 matched KT66 tubes $70.00
https://www.ebay.com/i/161982811986?chn=ps&dispItem=1

Total $321, Not as bad as I had stated before !! but I don't know if 12au7 or EV5 will need replacing

thanks

 

[wcarroll]

rossm, Original transformers for the W5M show up on eBay periodically. Seems like the last I saw went for a good bit less than $100.
With patience you may be able to find a good one for less money.

 

[Redboy]

I used a 6L6 as a rectifier for a VERY brief moment. They sound... awful that way. Once I got the right tubes in the correct sockets again, everything was better.

 

[Dandy]

Use a 5AR4 rectifier (new make) instead of what you have, and wait for a replacement PT to show up. You should be able to get cheaper multi section caps, or restuff the originals for less. The schematic calls for 450V caps which are common and cheaper. Single caps of 22uF and 47uF at that voltage will work fine for restuffing those cans (two inside the original can and one below). If you don't want to restuff, go for JJ multisection caps one 20 20 20 20 and one 50 50, and add one 47uF cap below.