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Re: swapping 5881's into an el34 amp?

Posted by Steve O (A) on January 28, 2007 at 05:50:27

In Reply to: swapping 5881's into an el34 amp? posted by stuck.wilson@gmail.com on January 28, 2007 at 05:13:21:

An HF87 will exceed the plate voltage and plate dissipation ratings of a true 5881 as you surmise so I would expect problems with this sub unless you mod the amp. The HF87 runs the output tubes pretty hard.

The 5881 is rated at 400V and 20W max while the EL34/6CA7 is rated at 800V and 25W. Personally, I totally ignore the 800V spec. I think you'll run into problems at anything greater than 450-500V with current prodution and most old stock el34s unless special provisions are made to handle this voltage (GE 6CA7s are possible exception here)

There are alternatives that would be mostly plug-n-play: Use the 6L6GC instead. The 6L6GC is the same as a 5881 in most important parameters but with hgher plate voltage and dissipation ratings 500V/30W). Another possibility would be the use of Sylvania/Phillips ECG 5881/6L6GBs from their last run (late 80s I think). These are really 6L6GCs in a smaller envelope to comply with the physical dimension specs of a 5881. The problem here is that you must be savy enough to be able to determine that you have one of these uprated 5881s. Angela has had them in the past and there are other sources too.

If I was in your situation I'd be inclined to stick with EL34/6CA7s. There are tonnes of EL34s out there to play with if true pentode operation is what you want. The GE 6CA7 is a beam tetrode as is the 6L6/5881 so that can be your contrast to a true pentode.

Regardless, be careful so you don't damage a nice amp.

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