Been doing some more work on my B77 recently to resolve a few issue’s
I was getting a regular wow from it that I put down to the capstan roller wheel as it was a bit tired but when I got a new one the problem was still there after cleaning the whole tape drive. I thought it might be some oscillation from the capstan drive motor board so I checked out the electrolytics I recapped this board with and they were just general purpose ones from a A77 service kit I bought a while back but they had very low ESR, so I decided to change them back to some new AVX tantalums that I had and this has cured the problem.
Capstan drive board by Alan Towell, on Flickr
Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, Micro Sieki MA505 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20, Revox A77, B77, PR99, TEAC X1000 & 3440, Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Avondale NCC300 Mono Block, Speakers Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500