[dconant]

Hello, Working on a Westinghouse H104. Been recapped and all the usual stuff. Plays very nice. My question is does this radio really need a 5U4 rectifier tube? Sounds like overkill. Wondering if I could sub in a lighter rectifier? If so what would I use? This radio makes a lot of heat. 

Tube lineup;
2 6Y6 push pull
2 6SK7
1 6SA7
1 6SF7
1 5U4

Schematic here. http://www.nostalgiaair.org/PagesByModel...024229.pdf

[morzh]

Q: Why not use 5U4? Problem with procurement? If not, I usually do not question the existing arrangement.
Also this would likely involve a different socket / rewiring, and you need the same filament voltage and similar current.

[dconant]

While on the subject of tubes the radio came to me with 6V6s (2) installed which should have been 6Y6s. Both work so I wonder which set would be better. My spare 6Y6s are a little tired so I leave them as test tubes in case I run across a dead one.

[TV MAN]

6V6's are beefier than 6Y6's are. They can use higher voltages & currents, but are also more pricey to buy. The Russian versions work well and can be had reasonable. A 5AR4 can sub for a 5U4, (it will raise your B+ so be careful) are smaller and use less heater current, but are more expensive to buy. A 5U4 is filament hungry and might be stressing your power trans. A 5Y3 will plug in but IS lighter. It might red plate (fuse). You can check your current draw across the resistor between your main filter caps by measuring your voltage and using ohms law. Then you can look up the specs online and see if it's within tollerance. Also, has this been recapped? If the coupler caps to the 6V6's is leaky, they will be drawing more current than what they should, causing things to run hot. This might be why you are finding heavier tubes in place of the originals - to "fix" an over current situation instead of fixing the problem. You should have either a negative voltage or 0 on the control grid of your output tubes. A + voltage means you have leaky coupling cap. I'd check this 1st. It might be the root of your problem.

Edit: Also a leaky or shorted cathode bypass cap (electrolytic) can mess up your bias on your 6V6s.

[dconant]

The set has been recapped and most resistors replaced as being out of spec. I shoot for 10%. I have 47s in place of 40 E caps. The grid voltage on 6V6 is +.6 volts. Plates are at 200 volts. Screens are 150 volts. Cathodes are at 8 volts vs 14 volts per the schematic. If I use good (stole from another radio) 6Y6s the grid voltages are 0 volts. Readings are with a VTVM. There is no resistor between the two main caps unless you count the field coil. The field coil is 167 ohms and the drop is 20 volts. So that would be 120ma for 6V6s? With the good 6Y6s the current is 162ma Seems like the 5Y3 is cutting it close. Guess I'll stay with the 5U4.

So why is there +.6 volts on the grids of the 6V6s? The schematic says the grids should be 0 volts. The 6V6s test good.

The 6Y6s are drawing more current so maybe I'd be better off with the 6V6s? AC current is up too. I guess it would be if DC current is higher.

[Arran]

From what I recall A 6Y6 gas a lower maximum plate voltage, 200 VDC, but draws more heater/filament current then a 6V6, 1.25 amps verses .45 amps for the latter, so the net result may be that the heater voltage might be slightly higher for the whole set. I think I would just procure some more 6Y6s, they are not a particularly expensive tube. From what I read the 6Y6G was developed for use in TV sets, one of the first specifically designed for it prior to the war, but I have only found them used in a handful of radios, one being a Canadian Westinghouse 754, another being a U.S General Electric H-116, I have a feeling that your Westinghouse might be similar to the H-116 other then the choice of a 5U4G rather then twin 5Y3s like the G.E has.
Regards
Arran

[dconant]

I think I will stay with the 6Y6s but I would like to know why the 6V6 grid measures +.6 volts and the 6Y6s are zero volts.

[MrFixr55]

From the schematic, I think that the 2 6Y6s in this set are in parallel, not push-pull. Look at the output transformer. there are only 2 leads. The plates connect to the transformer through resistors. The grids of both 6Y6s connect to the plate of the 1st AF tube through caps. I have not seen many radios that se this tube. Id develops rather high power at rather low voltage and rather low impedance.

The 6Y6 has a very low load resistance (2600 Ohms). 2 of these in parallel have a load resistance of 1300 Ohms. Plate dissipation at 200V is 12W and max output at 200V is 6.5W for one tube. This is 6L6 territory. These tubes run at lower plate voltage than 6L6 or 6V6 but much higher current. IMHO, the 5U4 is justified, and plate dissipation of 24W in Class A (and remember, that even at idle, there is high plate current in Class A), the 5U4 is justified.

[dconant]

Thank you for the info MrFixr. This is one hot running radio. Plays quite nice when both 6Y6 tubes are working. I didn't realize one was doing poorly until i swapped in another set.

[radiorich]

hello Arran,
Yes , I learned that too years ago about 6Y6 used in Tv's and you just don't see that tube used alot .
My General Electric console uses two 6V6's in a push-pull arangement and man does that set sound good .



Sincerely richard

[MrFixr55]

It is rare to see output tubes in parallel as opposed to Push-Pull. Push Pull eliminates even harmonic distortion. However, there are some, including pipe organ builders and RCA engineers, that believe that even order harmonics are "euphonic", ie pleasant sounding. This is why there is a niche hobby for SE (Single End) tube amps.

[RodB]

The farm radio I'm fixing right now has two 3Q5s in parallel. It's the first time I've seen it.

[morzh]

I think, because of smaller (real small, like 25%) efficiency of a Class A amp in a typical arrangement (theoretical inductive coupled is 50% but....), using two tubes in parallel allows to achieve somewhat decent power output.

[MrFixr55]

Push Pull does better, but requires a method of phase inversion. This costs money. I have a Coronado battery farm set (2V A, 90V B), sold by Gamble Skogmo, a Midwest chain store, that had 2 950s in parallel. I need an output transformer and still have to make the oscillator work (mice ate the coil).

The 3Q5 develops about 250mW, so 2 of these will give you 500mW. The standard AA5 AC-DC set develops about 1 to 1.5W

I have 2 RCA Farm Sets 5BT and 6BT, that run on a 2V A Battery, 135V B Battery and -7.5V C Battery. These sets have push pull Class B outputs (a 19 for the 5BT and 2 49s for the 6BT. Each set puts out about 2W into an 8" speaker.