EL84 power valves, who doesn't love them? With a good implementation they can be stunning, as is the case with the Croft 5C.

It's a bit of a brute of an amplifier, very minimalist looks but a very solid case.




It employs 8 EL84's in parallel push pull, rated very conservatively at 30W per channel but capable of 45W.

The one small fly in the ointment was the discovery that the case wasn't connected to the earth terminal of the IEC input, hence why the safety alert. This is a must with this type of equipment, so any owner please check this or have it checked.
Here is the correct connection to a dedicated screw/tag on the chassis, with the paint removed and serrated washers to ensure good contact.





Another small problem occurred at switch on, I must have just caught the max swing on the mains. The mains transformer is a toroidal type and as many of you will know they can have very large switch on surges, particularly if no surge suppression is present, as in this case.
The subsequent arc within the on/off switch was large enough to flash over to the other pole of the switch and blow the mains fuse and trip the RCB in the consumer unit.
I think this was an unluckily timed occurrence but I have also changed the switch for a better rated one.





Now everything is up and running listening can commence. As with any traditional valve amplifier the biggest arbiter of ultimate quality is the output transformer, with the 5C this hasn't been skimped on with some large quality units fitted.




The circuit appears to be 'ultra linear' with tappings for the grid 2 connections on the output valves. As stated with the full complement of valves the output power is commendable but with a large heat output, so the case gets very warm with extended use.




How does it sound you ask? Sublime.
There is a real 'valve' organic texture to the presentation, a superb open fluidity to the music. I know the frequency response is very wide, due in large part to the quality transformers, so you are presented with a very full sound with nothing missing.


A possible side benefit of using parallel output valves is that half of them can be removed and the amplifier still functions, of course with a reduced output power. Due to the different loading now presented to only one pair of output valves some crossover distortion is seen at high output, but an output of 18W is still achieved before this occurs.
This arrangement could be of benefit if the full complement heat output was excessive for the particular installation arrangements.
Half complement of output valves:




Delving a little deeper into the specific design revealed a fixed bias applied to all output valves, namely -12V. Now whilst excellent operation is to be had with new or good condition valves fitted, it can be a problem when the valves become tired or near their end of useful life.
I have known this arrangement to blow the HT fuse after a period of operation when the current flow through the tired valve(s) continues to increase with no limiting due to the fixed bias.
For this reason I have converted this 5C to auto bias on all output valves, which will ensure a long trouble free use.




A really stunning sounding power amp from 2003 I believe.