Philips N4305 reel to reel recorder/player very quiet

[Kigma01]

Hi everyone, I'm here in regards to my portable reel to reel tape player, a Philips N4305. I've finally got it to work after about 5 months of on-and-off fiddling around with the pots, belts and mechanical parts.
(I assume that) it records fine but playback is terrible. It's so quiet you have to put your ear right up to the speaker to hear even the faintest hint that there's anything on the tape. I have used several different reels and they all yield the same result. Also since the last time I used it, it's got even quieter!
I know it's not a problem with the speaker as the player has several audio inputs that when connected to, play fine out of it.
I've cleaned the heads with alcohol and cotton swabs (or q-tips, whatever floats your boat) and there's been no change. So here's my question: What would cause this faint-ness? Is it a problem with the playback head? If so, would it be a simple fix? If not, what else could've gone wrong?

[Jimmyhaflinger]

try cleaning the rec/play switch with and the track selector switch with contact cleaner

also look for fine cracks in the printed board, they easily happen if the chassis ever gets out of the cabinet as its weight then rests on the printed board

also look for broken connections to the head

[ben]

If this is the transistorized model then your sound problem is almost certainly leaky germainum transistors in the internal amp. Last year I did a couple of Philips machines of this vintage and both had the same fault.

[Jimmyhaflinger]

i have several of these machines but i had to replace just one transistor, it still worked but had lots of loud burst noise

[Maarten]

I think this one is all silicon. So possibly one or more noisy lockfit transistors or noisy black legged Japanese transistors.

[Jimmyhaflinger]

The N4305 is just a slightly facelifted 1967 version of the 1965 EL3553 and has the same all-germanium amplifier