6V6 to el84 tube adapter?

[Spud]

https://reverb.com/item/1382315-vht-av-sp-ad-special-6-el84-6v6-to-el84-tube-adapter-change-a-6v6-tube-to-a-el84-tube?bk=eyJhbGciOiJIUzI1NiJ9.eyJqdGkiOiJjMzlhMzNjNS0zYTE1LTQwMzAtOTg5NC0zNmI4MmQ4MmJiMzEiLCJpYXQiOjE3MzA1NzE0MTcsInVzZXJfaWQiOiIiLCJzZXNzaW9uX2lkIjoiIiwiY29va2llX2lkIjoiYzAzZjhlYjgtNGJhOC00YTk3LWE0NGUtZmJlYjBlZTA5OTIwIiwicHJvZHVjdF9pZCI6IjEzODIzMTUiLCJzb3VyY2UiOiJOT05FIn0.kQnEWb6JylQo2R59qEQk6afOcCBgon2JL5pFBSKzCYY

Can these be used in a Princeton style amp?

 

[TBurst Std]

Paging Mayfly
While it converts pins, I’m not current on the primary transformer requirements between the 2 types

 

[Spud]

Paging Mayfly
While it converts pins, I’m not current on the primary transformer requirements between the 2 types

I think they may be ok, they may require more heater voltage, but I am running a Weber copper cap so extra is available. As long as I re-bias would they be ok? Help! Well, I ordered the adapters. I hope they work. I am down to 3 6V6 tubes, but have 4 sets of EL84's but no longer have an amp for them. Just trying to save some dough.

 

[Spud]

Mayfly won't you help.........puhleeeeeeeeeeeeeeez!

 

[mayfly]

Hi there,

Well, I would not be too worried about the output transformer / load impedance that the tube sees.

But I would be concerned about the plate voltage and resulting bias power dissipation. The EL84 data sheet says that the tube's maximum plate voltage is 250V, although I have pushed this to 300V in cathode biased amps. If your amp is a typical to a fender Princeton it will have more like 400+V on the plates. Also note that the Princeton is a fixed bias amp. The EL84 can only handle 12W of plate dissipation at idle, so you'll have to have a way of measuring this and adjusting the bias to keep the tubes happy. If your tubes can survive that 400V plate voltage that is. Note that the Princeton uses a bias wiggle tremolo so the bias voltage is typically not adjustable.

Bottom line is that the Princeton is designed specifically for 6V6 tubes. EL84 is a different animal and although sounds great if treated right, it really is not nearly as robust as the 6V6. This is due to the smaller package and (supposedly) lower vacuum which in turn causes the lower allowable plate voltage and lower maximum dissipation.

Have fun. Don't light the place on fire

 

[mayfly]

oh - and the EL84 is unique among power tubes as it actually has some voltage gain. If you want to take advantage of this, disconnect the feedback loop.

 

[Spud]

Thank you sir. I will effectively reduce the plate voltage by using a 5Y3. I also may bite the bullet and order more 6V6's.

 

[mayfly]

Please measure the plate voltages once you've got it running. I question if the 5Y3 will give you the ~100V voltage drop you'll need.

 

[Spud]

Please measure the plate voltages once you've got it running. I question if the 5Y3 will give you the ~100V voltage drop you'll need.

I will measure the voltage. The other thing is this amp is an oddball (Marsh Buffalo Reverb) supposedly a Brownface 6G2 with tube reverb and a Master volume added.( I nixed the master for a Vox style treble cut).

 

[Spud]

Well heck, even with 5Y3 in I am measuring 400 volts at pin 3. I have it biased super cold at 14.5 Ma per tube (which probably makes the plate voltage higher) I am going to scrap the adapter idea, and get more 6V6's. I am going to leave the 5Y3 in though I think. I am out 40 bucks for the adapters. I will keep them in a parts chest and take them out and occasionally admire and fondle them. lol