This Hughes & Kettner repair is a tube 50 brought in for a valve amp bias. The Tube 50 is a fixed bias amp, meaning you need to bring the amp to a tech to have it adjusted (confusingly!!) by a technician. The opposite of fixed valve bias is cathode valve bias. Confusingly cathode bias is not usually adjustable. To make sense of this, check out this article
The Tube 50 is a 2 channel valve amp with three ECC83 in the preamp and two EL34s in the power amp. My apologies – the image is a stock image – not the actual Hughes & Kettner Repair.
If you have a Hughes & Kettner repair or a valve amp bias job, please get in touch.