Help with replacement 6BQ5/EL84

[joebog1]

Thanks Paul JD,
Especially for the circuit. As I stated in I think my first post, its a standard 4X 6BQ5 amp. I have repaired many over the years, of all makes. I will post more "stuff" as I can. I am off till friday ( cataract surgery) so there will be nothing till then.
Thanks again to all.

Joe

[ricard]

Originally Posted by G8HQP Dave

PL84 is 300mA heater version of EL86, which can be regarded as the low impedance (i.e. lower HT rail voltage) version of EL84 - might need some bias adjustment.

Curious, one would have thought the series heater version of the EL86 would have been called PL86 of course. Although there are other examples of valves where the first letter apparently affects more than the heater voltage - the EM71 and DM71 come to mind which although both indicator valves are massively different in their construction! Makes me wonder why they didn't want to adhere to common practice for certain particular valves. After all, it's true for most valves such as ECC85 - UCC85, isn't it?

[ColinTheAmpMan1]

Originally Posted by Paul JD

The OP does not say what model the amp is but it is certainly not the Laney 100H which is a 100 watt amp that uses 4 x EL34's. He described it as a Vox style circuit, this would suggest either the Laney VC15 which is a cathode biased 15 watt amp with 2 x EL84's or the Laney VC30 which is a cathode biased 30 watt amp with 4 x EL84's (these are very similar to the Vox AC15 and AC30 circuits).

My point was that assumption that the OP's amp was cathode-biased could be erroneous. The circuit I have is in "The Tube Amp Book - Deluxe Revised Edition" by Aspen Pittman. Admittedly there isn't much information on Laney Amps (nor EL84/6BQ5 valves).
Colin.

[Paul JD]

Originally Posted by ColinTheAmpMan1

My point was that assumption that the OP's amp was cathode-biased could be erroneous. The circuit I have is in "The Tube Amp Book - Deluxe Revised Edition" by Aspen Pittman. Admittedly there isn't much information on Laney Amps (nor EL84/6BQ5 valves).
Colin.

The description of the amp as an EL84 based Laney that is similar to a Vox essentially ruled it out as being anything other than cathode biased. Vox have never produced a fixed bias EL84 amp and to the best of my knowledge neither have Laney. In fact 99% of EL84 based guitar amps will be cathode biased, in 35+ years of working on guitar amps I have only ever encountered two fixed bias EL84 amps and neither of those was made by Laney! Fixed bias tends to be used only on higher powered amps (typically 40 watts and above) and those will be using octal power valves, EL34, 6L6, KT66 etc.

In any case if you read my post you will notice that I did put a question mark after the assumption

[Maarten]

Originally Posted by ricard

Curious, one would have thought the series heater version of the EL86 would have been called PL86 of course. Although there are other examples of valves where the first letter apparently affects more than the heater voltage

To complicate things, the American numbers are xCW5 for all EL86 variants except UL84, suggesting that the UL84 may be the odd one out amongst odd tubes. It might have been the prototype for the series.

[G8HQP Dave]

Another 'gotcha' is PCL83 vs ECL83. The pentodes are the same, but the triodes are different.